I have been having this same problem on and off for a while now, across 3 separate company files.

Today I stumbled upon something...

Do you have a lot of reports showing under your "Memorized Reports" list?

I had a bunch of old reports I wasn't using anymore, so I deleted out a bunch. I also created a new group "Misc. Reports" 
And I went to pull the report I've been wanting to memorize for AGES... and just for the heck of it, I tried to memorize it to the new folder I just created... and... IT WORKED!

Not sure what accounting god decided to smile on me today, but I'll take this as a win.