Hi,
Since you now have MPLAB 8.87 installed make sure you point MCS to the MAPSMWIN.EXE installed with THAT version instead of the "original" (or copied) one in C:\MPASM, there might be other support files in the new MPLAB installation that's needed so simply copying the "new" MPASMWIN.EXE into the old installation might not be enough.

If all fails uninstall ALL MPLAB installations and reinstall 8.87 to its default location (don't just install MPASM), then make sure the assembler selction in MCS points to that location.

/Henrik.