Cannot open file

Hi ArgoUML community,
 
i cannot open an my project any more. I've been working on that project file for almost half a year
and used ArgoUML 0.24 for this. Sometimes I also used the Eclipse plugin ArgoEclipse, which is the
0.22 release.
 
A few days ago I started to use 0.26 over Java web start. Since then I cannot open my project file
anymore, no matter which version I use. When trying to open with 0.24 or 0.22 I get the short error
message "dialog.error.file.version". When trying to open with 0.26 I get a much longer error. I
pasted this error here: http://dpaste.com/90426/
 
Can anybody help me opening the file again? Any hint is appreciated.
 
Thanks folks,
Anh Tu