Memory Issues PIC

Hello
I wrote a program in MikroC for PIC16F877A. it worked correctly but i had to make some additions to the functionality. I observed that when the used ROM reached 30% the program stopped working in Prodeus with error of "Stack overflow during CALL" Operation ".

I thought it is better to switch controller and found pin compatible controller PIC18F452. I converted that same program to this controller but now when the memory of this controller reaches to approximately 14% i start to get "Attempt to execute Illegal Opcode {loaded from PC= various numbers here}, instruction executes as NOP".

What could be the problem. I cant figure it out. Is it Proteus or is it MikroC that is why i planed to switch to MPLAB to check it out but that is real boring IDE. What can it be?

I observed that when the used ROM reached 30% the program stopped working in Prodeus with error of "Stack overflow during CALL" Operation ".

Afnan

"Stack overflow during CALL" Operation ". has nothing to do with rom size.

PIC devices use a hardware stack.
In the 16f877 it is only 8 levels so you are limited as to how many nested subroutines
calls you can make.
The 18F452 allows up to 31 nested calls, but it may be the same problem.

The limit includes subroutine calls and interrupt handlers.

Well i was not considering limitation on subroutine (functions) calls. In my file i tried to make modular look and made many sub functions to isolate the different logic. Can this be the problem?

Any of the below reasons:
1. you might be using bigger local variables e.g. buffers in your functions.
2. too many function calls
3. Stack pointer not initialized properly (less probable)