Try to use the internal USART, you must use HSERIN instead of SERIN. If you want to be sure to not overflow the input buffer add

DEFINE HSER_CLROERR 1

at the begining of your program.


For the noise... have you any pull down/Pull up resistor on the RX pin of your PIC. Do you use MAX232 ???

"At the weekend I begin to change the librarys of PBP !"
Must be sure that's the problem before...!!! I'm pretty curious to see your code and schematics before.