[Lazarus] Can't find unit contnrs used by Masks

[Michael Schnell]

"Recompiling contnrs, checksum changed for System
   masks.pas(29,22) Fatal: Can't find unit contnrs used by Masks"

Since many weeks I get this error when trying to recompile the newest 
svn version of Lazarus with the newest svn Version of FPC.

I remember that I once had this problem and it was solved by using a 
more recent FPC.

Will this problem be solved with a later version of either Lazarus or 
FPC or do I do something wrong ?

-Michael