I've not had any problems over the last 6 months or so up until the last few times I've tried to upload a particular sketch.
The problem I'm currently having is that I get a "verification error; content mismatch" message every time I try to upload a particular sketch.
This has been tested with 2 Arduino Diecimilas. 1 Heavily used and one hardly used and they both report failures in the same place so I don't think its anything to do with the flash being worn out.
I think it may actually be due to the code I'm trying to upload as the code contains a font (using progmem) which will set over 256 bytes to 0xFF in one long chunk. commenting out the font causes the upload to work successfully.
My current working theory is that the long string of 1s being sent over serial is causing the sender and receiver to lose sync due to a timing issue.
I would try rearranging the font so that it doesn't have the long block of 1s in a large chunk but unfortunately the code I'm working on is time sensitive and I had to rearrange the font already so that I could access it more quickly.
Can anyone think of a work around (other than change font)? Is there any way to get the arduino bootloader to do serial comms at a slower rate?