java - Why tests sometimes build failed (maven-surefire-plugin)? -

in netbeans wrote projects using selenium. projects build ok, build falied. think, problem in maven-sunfire-plugins. why 48 builds 3-4 failed?

in jenkins console see:

org.apache.maven.surefire.util.surefirereflectionexception:  java.lang.reflect.invocationtargetexception; nested exception           java.lang.reflect.invocationtargetexception: null 

pom file

<project xmlns="http://maven.apache.org/pom/4.0.0" xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"     xsi:schemalocation="http://maven.apache.org/pom/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">     <modelversion>4.0.0</modelversion>      <groupid>pl.com.mycompany.test</groupid>     <artifactid>selenium-test</artifactid>     <version>1.0-snapshot</version>     <packaging>jar</packaging>      <name>selenium-test</name>     <url>http://maven.apache.org</url>      <repositories>         <repository>             <id>central</id>             <url>http://maven-repo.myportal.pl:3080/artifactory/repo</url>             <snapshots>                 <enabled>false</enabled>             </snapshots>         </repository>         <repository>             <id>snapshots</id>             <url>http://maven-repo.myportal.pl:3080/artifactory/repo</url>             <releases>                 <enabled>false</enabled>             </releases>         </repository>         <repository>             <id>internal</id>             <name>archiva managed internal repository</name>             <url>http://maven-repo.myportal.pl:3080/archiva/repository/internal</url>             <releases>                 <enabled>true</enabled>             </releases>             <snapshots>                 <enabled>false</enabled>             </snapshots>         </repository>     </repositories>      <properties>         <project.build.sourceencoding>utf-8</project.build.sourceencoding>     </properties>      <build>         <finalname>selenium-test</finalname>         <plugins>             <plugin>                 <groupid>org.apache.maven.plugins</groupid>                 <artifactid>maven-compiler-plugin</artifactid>                 <version>2.0.2</version>                 <configuration>                     <compilerversion>1.6</compilerversion>                     <source>1.6</source>                     <target>1.6</target>                     <!--<encoding>cp1250</encoding> -->                     <encoding>utf-8</encoding>                     <!--<encoding>iso-8859-2</encoding> -->                 </configuration>             </plugin>         </plugins>     </build>      <dependencies>         <dependency>             <groupid>oracle</groupid>             <artifactid>ojdbc</artifactid>             <version>1.4</version>         </dependency>         <dependency>             <groupid>commons-logging</groupid>             <artifactid>commons-logging</artifactid>             <version>1.1.1</version>         </dependency>         <dependency>             <groupid>commons-lang</groupid>             <artifactid>commons-lang</artifactid>             <version>2.4</version>         </dependency>         <dependency>             <groupid>commons-dbcp</groupid>             <artifactid>commons-dbcp</artifactid>             <version>1.4</version>         </dependency>          <!-- selenium -->         <dependency>             <groupid>org.seleniumhq.selenium</groupid>             <artifactid>selenium-java</artifactid>             <version>2.43.1</version>         </dependency>         <dependency>             <groupid>pl.com.mycompany.selenium.util</groupid>             <artifactid>selenium-listener</artifactid>             <version>release</version>         </dependency>         <dependency>             <groupid>org.apache.maven.plugins</groupid>             <artifactid>maven-surefire-plugin</artifactid>             <version>2.11</version>         </dependency>         <dependency>             <groupid>org.jsoup</groupid>             <artifactid>jsoup</artifactid>             <version>1.6.1</version>             <scope>provided</scope>         </dependency>          <dependency>             <groupid>pl.com.mycompany.portal</groupid>             <artifactid>commons-portal</artifactid>             <version>release</version>         </dependency>          <dependency>             <groupid>weblogic</groupid>             <artifactid>weblogic</artifactid>             <version>8.0</version>         </dependency>          <!-- tests -->         <dependency>             <groupid>junit</groupid>             <artifactid>junit</artifactid>             <version>4.9</version>             <scope>test</scope>         </dependency>         <dependency>             <groupid>org.easytesting</groupid>             <artifactid>fest-assert</artifactid>             <version>1.4</version>             <scope>test</scope>         </dependency>         <dependency>             <groupid>org.testng</groupid>             <artifactid>testng</artifactid>             <version>6.8</version>             <scope>test</scope>         </dependency>     </dependencies>     <!-- -->     <profiles>         <profile>             <id>2db</id>             <build>                 <plugins>                     <plugin>                         <groupid>org.apache.maven.plugins</groupid>                         <artifactid>maven-surefire-plugin</artifactid>                         <version>2.11</version>                         <configuration>                             <properties>                                 <property>                                     <name>listener</name>                                     <value>pl.com.mycompany.selenium.util.testngrunsuitelistener</value>                                 </property>                             </properties>                             <systemproperties>                                 <property>                                     <name>job_name</name>                                     <value>${project.artifactid}</value>                                 </property>                             </systemproperties>                              <testfailureignore>true</testfailureignore>                          </configuration>                     </plugin>                 </plugins>             </build>         </profile>     </profiles> </project> 

oddest lot of builds okey. 48 builds 3 throw , don't understand why. error?