I also got this message in my project, but I was able to fix it by commenting out the following line in my lpr file:
{$IFDEF WINDOWS}{$R cajasuc3.rc}{$ENDIF}
This just happened with the latest daily Lazarus snapshot.
It would be good if the message was a bit more informative. Should it be reported in the bug tracker? If so which one, the Lazarus or FPC?