[rules-users] ClassCastException: MVELDialectConfiguration cannot be cast to DialectConfiguration

Hy I get the following error: ...    Caused by: org.drools.RuntimeDroolsException: Unable to load dialect 'org.drools.rule.builder.dialect.mvel.MVELDialectConfiguration:mvel:org.drools.rule.builder.dialect.mvel.MVELDialectConfiguration'         at org.drools.compiler.PackageBuilderConfiguration.addDialect(PackageBuilderConfiguration.java:313)         ...         ... 42 more     Caused by: java.lang.ClassCastException: org.drools.rule.builder.dialect.mvel.MVELDialectConfiguration cannot be cast to org.drools.compiler.DialectConfiguration         at org.drools.compiler.PackageBuilderConfiguration.addDialect(PackageBuilderConfiguration.java:308)         ... 51 more I'm using drools in a maven project, pom.xml: ...     <dependency>         <groupId>org.drools</groupId>         <artifactId>drools-compiler</artifactId>         <version>5.5.0.Final</version>     </dependency>     <dependency>         <groupId>org.drools</groupId>         <artifactId>drools-core</artifactId>         <version>5.5.0.Final</version>     </dependency> ... What could cause this error? Thanks for your help. Kind regards, Peter