It will get stuck at while(UIP) as there is nothing changing the state of UIP. It seems that you are trying to wait until the MSB of XBYTE[10] is cleared before continuing. If this is the case you need to do:

UIP = XBYTE[10] & 0x80;    // Initialize UIP
while (UIP)                // Wait until UIP MSB is cleared
   UIP = XBYTE[10] & 0x80; // Read MSB of XBYTE[10] into UIP