Please help me out...
Debug build of project `C:\Users\SYED SHAHBUDDIN\Desktop\new\xyz.mcp' started.
Preprocessor symbol `__DEBUG' is defined.
Mon Oct 07 20:24:06 2013
----------------------------------------------------------------------
Clean: Deleting intermediary and output files.
Clean: Done.
Executing: "C:\MCC18\UNWISE.EXE" -p=18F458 "xyz.c" -fo="xyz.o" -D__DEBUG -Ou- -Ot- -Ob- -Op- -Or- -Od- -Opa-
Could not spawn language tool. Check command-line options. (740)
A language-plugin exception occurred and was logged.
----------------------------------------------------------------------
Debug build of project `C:\Users\SYED SHAHBUDDIN\Desktop\new\xyz.mcp' failed.
Preprocessor symbol `__DEBUG' is defined.
Mon Oct 07 20:24:06 2013
----------------------------------------------------------------------
BUILD FAILED

 

It looks like you need to specify the compiler in mplab.

Try giving more information whenever you ask a question...

 

Your compiler exe is called UNWISE?

 

MPLAB has lost your compiler. It's happened to me a few times too.

Sometimes you can close the project (try not to save it), close and restart MPLAB and see if that helps. You may also try changing the tool suite (under the project menu) to something else, then back to the correct one to pin it down.

If that doesn't help, then as a last resort I reconstruct the project from scratch.