Under View > Compile and Program Options > Assembler tab ...
Is the path above the Find buttons ... C:\Program Files\Microchip\MPASM Suite or C:\Program Files (x86)\Microchip\MPASM Suite for 64-bit systems?

If not, click the Find manually button and point it there.
MicroCode Studio will usually find the wrong path if you have more than one MPASMWIN on your computer.