HotA - General Questions and Discussions

From the .lod file of HotA 1.38, I extracted 2 campaigns and used the campaign editor to extract the maps from them – there were no problems. When I decided to do the same with 3 campaigns from HotA 1.42, the campaign editor gives an error message about a version mismatch between the campaigns and its own version (or that the campaign files are not what the editor opens) – something like that. HotA doesn't have its own campaign editor, so I must have opened them with the one from Shades of Darkness before. What's the problem, and what can I use to open the new campaign?
The following message appears: "The file 'Hota0206.h3m' has an invalid format. It is impossible to import. Invalid or corrupted campaign file!"
Why .h3m and not .h3c? After all, the file has the .h3c format.