That's probably the problem - you need fpc.cfg for 2.5.1 because you set it to be the compiler you use to compiler projects. Just copy fpc.cfg from 2.4.2 to 2.5.1 and replace all 2.4.2 with 2.5.1. Also, point FPC source directory to your SVN checkout-ed source of FPC (the source you compile with the above batch file). That should fix the problem.
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