avrdude: verification error; content mismatch on NANO ATmega 328p

Hello everybody, I was going to jump through the window, but first try to post my problem here, hoping any help... Thank you in advance. Arduino NANO on fedora-14 arduino-22 Like any love-relationship, at the beginning everything was roses and happiness: I could upload any program to the NANO-de-los-cojones. But one day I receive the "verification error", what changed? I don't know. I was working on arduino-MEGA at the same time, and perhaps once I forgot to change the board type in tools menu of the arduino IDE, and try to upload to the NANO when the MEGA was selected. I have tried different (almost all) upload velocities in preferences.txt The NANO is working and I can read from serial port data from the last program upload (in those beautiful times) so the FTDI chip looks to be also working. What does this "verification error" means? How can I solve the problem? How can I upload programs to the NANO again? Do I have to reburn the bootloader? How? Thank you very much

try this : connect NANO to PC press and hold reset button on nano hit upload while holding reset button when the information about sketch size shows up release the reset button

Have you tried loading a small example sketch like Blink?

Does you code have a large block of 0xFF bytes? Avrdude (the uploading program that Arduino uses) skips programming pages full of 0xFF because it told the chip to erase all pages to 0xFF. The bootloader DOESN'T do the full erase so a page of 0xFF gets left with whatever contents the last upload left it with (probably not all 0xFF). The verify then fails.