>could you please send me the exact input and output file for examination?
I just found the error: I was looking at the first "FINAL ENERGY" and then I jumped to the end of the file and searched backwards for the MP2 energy. This is OK in a single-point output, but I had mistakenly forgot to change runtyp from "optimize" to "energy". Therefore, I was comparing the first HF energy with the E(0) from a different geometry. I'm sorry for having "cried wolf" without good reason....