I've had this same problem about 3 or 4 times and I have a little information to offer:
1. I think it occurred after I used "Find in Files" and then clicked the Save button to save the .RC updates.
2. The original .RES file is untouched.
3. The resource file and other things are saveable.
4. I can open the .RC dialogs and print out pictures of them and then I write in the definitions as a means of recovering. It's interesting that you can print them.
5. I tried to save it under a different name, a different drive and it will not save the .RC once this error arises.
a. After you select the new folder for the .RC it goes to asking for a new folder for the .H resource file then after that it errors out.
6. It would be nice to have an RCBAK file created that is one step behind as a recovery measure or transfer the old .rc file into the recycle bin as an alternate recovery measure.
7. I had upgrade my PC to Windows 7 earlier this year, prior to that it never did this in XP.
I know how difficult it is to deal with any problem that is not easily reproducible, that is the nature of any program debugging. I hope that my information can be useful.
Regardless of occasional problems, I still find that Pelles C is an excellent program and I have been using it for several years now in measuring production airflow and the executables are running on several hundred Airflow machines around the world.