ClassNotFoundExcpetion when deserializing the Request

[stackpivot]

DSing the response works just fine, but when DSing the request this Exeptions is thrown:

java.lang.ClassNotFoundException: boolean
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
...

are you familiar with this problem? do you know how to fix it?

i'm using Burp 1.5.08, the current version of BurpJDser-ng and jre1.7