What computer operating system? I will assume Windows 7, 8, 8.1, or 10 64 bit for now. Are you running 9.0 as the 9.0.1 Update? If not, please use the following link for the update rather than an opened project's Help Menu/Updates. Adobe - Premiere Elements : For Windows : Premiere Elements 9.0.1 update
Lots of possibilities....
a. Did the letter of the backup drive change? Is the backup drive a network drive? Are the source media for each of these projects in the same save location that they were when copies of them were imported into the project....any moving, deleting, renaming of source media files and folder after the save close of these projects?
b. Do you have the latest version of QuickTime installed on your computer with 9.0/9.0.1, and are you running the programs as administrator (from user account with administrative privileges)?
c. Is your video card/driver version up to date according to the web site of the manufacturer of the card?
d. Does the problem exist with and without the antivirus and firewalls disabled?
e. Are you running the program with an Internet connection?
g. Windows Updates up to date?
Please consider, give more information, and then we can decide what next.
Any questions or need clarification on the above, please do not hesitate to ask.
Add On...Adobe Support for Premiere Elements is offered via online Adobe Chat and that is limited to current version (now 14).
Thanks for the quick response ATR. I have two swap-able drive bays for my backups. Once I swaped which bay the BU drive was in, all is well.
Great news "...all is well." Great job.
Best wishes moving forward with your Premiere Elements projects.