variables values changes unexpectly

I declare these variables:

unsigned long idata xpaquetes,xbytes;
unsigned long errors,PHY,CRC;

I ran my progran and after 3 minutes the errors,PHY and CRC variables change to
0xaaaaaaaaaaaaaaaa

but the xpaquetes and xbytes still have the right value?

I think something is wrong during compilation
because my program started counting and updating these variables but after few minutes these variables are unstable

what can I do?

I put now :

unsigned long xdata errors,PHY,CRC;

but I got the same error

please give me suggestions