mega2560 does not finish upload with no message


My old mega board won’t finish the upload of a new version of my program.
When uploading an old version or a basic example it does upload OK.

The upload starts with both versions the same with Rx and Tx LEDs blinking but with the new version, before the upload finishes, Rx and Tx stop the continuous blinking and start blinking once every 4 seconds while the IDE is stuck as in the picture below

On another (new) mega board both versions load and execute OK. Must i understand that the old mega is dead?

Some older MEGA boards have a built in 'monitor' which allows you to poke around in memory using serial commands. Unfortunately the 'monitor' was activated by any three '!' characters in a row. If your sketch (or a library your sketch includes) has three '!' characters in a row, the upload will freeze. Check your sketch.

Bingo! Thank you dear