I have encountered a dilemma that I hope someone knows of a solution for. Roughly 10-12 years ago I created a few disks full of files on my 800xl/1050. I then diskcomm'd them and uploaded them via modem to my pc. At the time I was using Atari800Win/Plus on the PC. I used that to convert the dcm files to atr files. Several years ago I switched to Altirra after finding some glitches with Atari800WinPlus in Windows7, and seeing that Atari800WinPlus was not being updated/maintained anymore.
Just now I went to use one of those atr disk images in Altirra for the first time. Obviously there must be some differences in "atr format", because Altirra will not accept any of the atr's I created in Atari800WinPlus. I am however able to open and use them in Atari800WinPlus, so it's not the case that the files have become corrupted, but that Altirra just doesn't recognize Atari800WinPlus's version of atr. I have also tried using the PC utility MakeATR, but that utility also will not open the atr's, saying they are corrupt.
Any ideas? Any way I can either convert the atr's to a version that Altirra likes, or extract the files from these atr's and then import them into a new blank atr disk using MakeATR?