Murat.

Perhaps you are experiencing a USART overrun condition in your ISR when you are reading the packet from the PC using "HSERIN".

I would try a couple of things to narrow this issue down.
1. Comment out the following line at the beginning of your code "DEFINE HSER_CLROERR 1".
Then add the following 3 lines in your ISR:
Code:
For i = 0 to 127
        if RCSTA.1 = 1 then  'Add this line  "OERR: Overrun Error bit"
            lcdout $fe,1,"Overrun Error: ", dec3 i  'Add this line
        endif  'Add this line
        HSERIN [HEX2 H[i]]
    next I
Doing this will let you know via your LCD if you are experiencing an overrun and at which byte position it occurred in.

2. If you are experiencing overruns, then lower your baud rate to 2400 and see if the problem stops.