Exception initializing velocity engine

Hi, I am trying to run mxmlc using Flex ant tasks. During execution, i run into the problem below. The ASTprocess class is in the mm-velocity-1.4.jar. I am using Flex SDK 3.0.0. Thanks in advance

[mxmlc] <...>\main.mxml: Error: Exception initializing velocity engine: flex2.compiler.util.VelocityManager$Logger
[mxmlc] Error: java.io.InvalidClassException: org.apache.velocity.runtime.parser.node.ASTprocess; org.apache.velocity.runtime.parser.node.ASTprocess; class invalid for deserialization
[mxmlc] java.lang.RuntimeException: java.io.InvalidClassException: org.apache.velocity.runtime.parser.node.ASTprocess; org.apache.velocity.runtime.parser.node.ASTprocess; class invalid for deserialization
[mxmlc] at flex2.compiler.util.VelocityManager.getTemplate(VelocityManager.java:175)
[mxmlc] at flex2.compiler.util.VelocityManager.getTemplate(VelocityManager.java:151)
[mxmlc] at flex2.compiler.util.VelocityManager.getTemplate(VelocityManager.java:137)
[mxmlc] at flex2.compiler.mxml.InterfaceCompiler.generateSkeleton(InterfaceCompiler.java:697)
[mxmlc] at flex2.compiler.mxml.InterfaceCompiler.parse2(InterfaceCompiler.java:280)
[mxmlc] at flex2.compiler.mxml.Compiler.parse2(Compiler.java:129)
[mxmlc] at flex2.compiler.API.parse2(API.java:2381)
[mxmlc] at flex2.compiler.API.parse2(API.java:2339)
[mxmlc] at flex2.compiler.API.batch2(API.java:373)
[mxmlc] at flex2.compiler.API.batch(API.java:1108)
[mxmlc] at flex2.compiler.API.compile(API.java:1281)
[mxmlc] at flex2.compiler.API.compile(API.java:1201)
[mxmlc] at flex2.tools.Compiler.mxmlc(Compiler.java:240)
[mxmlc] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[mxmlc] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
[mxmlc] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
[mxmlc] at java.lang.reflect.Method.invoke(Method.java:597)
[mxmlc] at flex.ant.FlexTask.executeInProcess(FlexTask.java:311)