GWT-2.5-COMPILE-ERRORS-README.txt

Serializeable classes were not given explicit serialVersionUID values and so are subject to JDK-choice. This may lead to mismatches and java.io.InvalidClassException during compilation of client.

Compile error stack trace example:
 
Caused by: java.io.InvalidClassException: com.google.gwt.dev.jjs.ast.JDeclaredType; local class incompatible: stream classdesc serialVersionUID = -8155793964565947646, local class serialVersionUID = -1052417216019896795

Please see http://code.google.com/p/google-web-toolkit/issues/detail?id=7530

recommended fix: 
 - run 'rm -rf gwt-unitCache' at the root of project source
 - compile with '-Dgwt.usearchives=false'