preview error

[dalu]

hi
im new to lyx and i'm trying to write an essay. im pretty satsfied but now
 an error occured.
the preview is not working anymore. none of it. i get an error that means 
"error with the preview of pdf2". 
i tried other formats but none of it is working. i'm pretty desperate and hope
 one of you could help me.
i don't know if it is of any importance, but i installed versions (svn) before.
thank you!