i always have trouble with this error i don't know the source. what can i do? i have tried Mcafee, doctor spy and Zoon Alarm but none of them worked. i get ride of this error by system restoring but after a wile the error come back again.

error:

16 bit MS-DOS subsystem
C:\WINDOWS\system32\systems.exe
the NTVDM CPU has encountered an illegal instruction.
CS:0ded IP:011d OP:2e 63 6f 6d 20 choose 'Close' to terminate the application.

buttons= Close(when i press the error window will be closed)
Ignore(when i press the error would be repeated just for one more time and then it would be closed).
please help me it's really bothering me.
actually nothing. it just pup-up every 5 minutes. when i run the exe file(C:\WINDOWS\system32\Systems.exe) this error would be show to me so i thing if i delete this file every thing would be OK but i can't delete it because it's being used by an other program.