Ok, I decided to just take a whirl at installing both this and Separate Unread PMs with installing this one first.
I'm going to assume you intended to post in the Search Sent PM mod thread, since you posted in the Separate Unread PMs mod thread....
Whoops. I was talking about the Edit Unread PMs and this mod. I got the 2 topics/mods mixed up so I can see where it was pretty confusing. Sorry about that. I never attempted to install the Search PMs yet.
Let me try this again. I installed Edit Unread PMs first and everything was fine. No errors in logs, etc. however I didn't actually test to see if things worked 100%. I never really have with any of your mods because they always just worked for me. I did have the newly added links(edit/unsend) so I figured everything was fine. I hit the logs again and still no errors after navigating around my PM box.
Then I installed this mod(Separate Unread PMs). That's where things went bad and is what I was talking about in my post above. Once Separate Unread PMs was installed I lost access to my inbox. I would click it and would just stay stuck in my sent folder. The outbox folder was exactly the same. I had 2 sent but unread messages and those were both just gone. They weren't in sent or in outbox. I started checking the code edits one by one but decided to uninstall for the time being and that's when it errored out. I manually made the change for the error(it was only one) and carried on. Went back to my inbox and I still couldn't access it. It was the same as it was with Separate Unread PMs installed. I go ahead and uninstall Edit Unread and everything is back to normal.
I didn't get any errors for either mod during install other than the aforementioned 2 that seemed related to the Post and PM Attachments mod which said ignore error when I installed Edit Unread PMs. My installation was pretty much:
1. install Edit Unread PMs
2. navigate PM box - both inbox/sent work
3. check for errors after
4. install Separate Unread PMs
5. go to inbox and can't get it
6. check for errors and see none
7. decide to uninstall Separate Unread and get an error
8. proceed and manually fix error after
9. inbox still broken
10. no errors in logs at all
11. uninstall Edit Unread PMs
12. everything works again