OK, call me stuid ...
I found the problem: there was no space left on the device :-(

Ingo Hohmann wrote:
> Hi to all Squeakers,
> 
> I have Problem with my sources, I have copied an image including sources 
> file from Linux to Windows, worked on it, and then copied it back, to 
> Linux, and got on with my work.
> 
> I created some methods on both systems, and now I get an error with one 
> specific method. Whenever I try to open this method I get the error:
> 
> "There may be a problem with your sources file!
> The source code for every selector should (usually) start with the 
> method selector, but this is not the case with this method!" (The error 
> text goes on for a while with explanations).
> 
> Does anyone have an idea what happened, and specifically what to do 
> about it?
> 
> To my knowledge I created this method after I copied the image etc. back 
> to Linux.
> 
> 
> Thanks for your help.
> 
> Ingo
>