Roberto,

Verify the signal integrity with a 'scope at the microcontroller. If the bit time of the 'U' isn't very close to the theoretical bit time for the baud rate you would like to use, the bootloader won't auto baud correctly and it won't work. My experience has been that UARTs will tolerate up to about 3% baud rate error. Get rid of FLIP and use FlashMagic. When you do get it to autobaud, measure the baud rate coming back out of the micro. It should be within 3% of the baud rate on your PC or you will have problems.

If it doesn't work one day and then works the next day without changing anything, you still have a problem, that is if you want your project to be reliable.

Cory Spackman