Sanjay:
You mentioned that you set the stack at 50H. And then you said that you started your data allocations at 30H. Do all of your global data and buffers fit in the space from 30H to 50H (32 or 33 bytes worth) ? If you have more data than that then you are putting your data in the stack area where pushes and calls will cause your data to be modified. Try moving the SP above all data. (Recall that SP grows upward on an 8052).

Michael Karas