Turns out one of my titles had too much (!) text in it, which caused the project file (the .pds file) to get corrupted due to truncation of the title. At the point where the title was truncated, an invalid character had been inserted into the project file, leading to buffer overrun when read by PD5 and a crash due to invalid memory access.
The project files are in some slightly deviated XML format - that is after removal of the header it is true XML format. Good XML readers like Eclipse (with XML plugin) can then read the file and test it for corruption. Or you can simply open the pds file in Notepad, search for all your titles and check them for truncation. Interestingly the Cyberlink customer support is not able to verify the integrity the project files generated by their own programs!
Anyways, if you run into this situation, search the project file for any invalid characters in your titles, remove them, save the file and you're good to go again.