I have closed my trouble ticket regarding this issue, with the following comments to Cyberlink...
The support person told me to uninstall, run provided cleanup scripts, re-install. I did this and the problem still exists. Reported same to support, which said to uninstall, run provided cleanup scripts, re-install. Replied already did it, no help. Support then replied uninstall, run provided cleanup scripts, re-install. I don't have any more time to help Cyberlink debug their program. I will go back to using standalone wave editors. Too bad, as the integrated wave editor (although deficient in functionality compared to mainstream wave editors, and those in other video editors) is a great idea which, if worked, would greatly simplify the process of improving the sound in video projects. Having to save the sound as a wav file, open it in another editor, save in other editor, then import back into PD9 at the correct timeline, would be eliminated.
P.S. I suspected that the wave editor having working directories on different drives than the project source might be causing the problem. So I created a simple test project that has everything on drive C:, including the WaveEditor working directories. No help, Still everything on the File menu grayed out, and attempting to return to PD9 gets "unable to save file" with return to PD9 and all wave edits lost.
One clue - WaveEditor was working fine (as supposed to) with no loss of edits returning to PD9 -BEFORE- upgrade to new WaveEditor that came with upgrade 2504. Problem began with 2504.
Alternative to Cyberlink WaveEditor: what would be better than the wave editor that comes with PD9, would be PD9 preference setting that allows user to choose their own Wave Editor, but works like PD9 in that can push an Edit Audio button, sound is sent to wave editor (of my choice), then exiting my Wave Editor returns to PD9 with sound track updated.
FYI: I have installed and used all the popular wave editors, including Audacity, Sony Sound Forge, AVS Audio Editor, and Magix Audio Cleaning Lab. I find that NCH WavePad Audio Editor is superior to all others to term of bang for the buck, ease of use, and functionality (there is a free version, but I own the Master verion). Even though I own Sound Forge, WavePad is the editor of choice for my needs (cleaning up noise, improving voice legibility, leveling sound levels) in video projects.