ATMEGA 2560 programing

Hi, I try to upload a sketch to a ATMEGA 2560 using the arduino IDE and get the following (after upload done....):

avrdude: verification error, first mismatch at byte 0x0634 0x0e != 0x06 avrdude: verification error; content mismatch

What can it be? Thanks

How old is the board?

Do you have !!! anywhere in your code (other than comments)?

The board is new (it is not an arduino board but I use the arduino IDE). Yes I have some Exclamation marks in the code. Why?

Another thing, some of the exclamation marks are for logic not calculation.

Some bootloaders use !!! as an "escape" to go into command mode.

Does it have to be 3 in a raw?