There's a known bug in ACDSee Pro, but the company has yet to address it.
If you install two identical drives, chances are that Windows will give them the same Volume Serial Number, in the form of XXXX-XXXX.
It turns out that ACDSee Pro keeps a database of all storage volumes using this supposedly "unique" Volume Serial Number. That's why if you perform a search for photos in ACDSee Pro, and try to view any one of the results in full screen, ACDSee Pro might give you an error that the file is missing and ask if you wish to remove the file from its database.
First we need to check that indeed there are two HDDs with the same Volume Serial Number.
NOTE: For this example, let's assume that you have installed a couple of identical 2TB WD HDDs, and they have been assigned the drive letters D: and E:.
1. Open CMD, and type D:.
2. Type: dir/w
The 2nd line will display the Volume Serial Number of D:.
3. Now type E:, and then dir/w,
The 2nd line will display the Volume Serial Number of E:.
4. If they have the same exact Volume Serial Number, then we need to download a small app from Microsoft called VolumeID (it can be run on WinXP and above).
5. Extract the Volumeid.exe file to E: (doesn't matter, any simple to remember path is OK).
6. Open CMD (if not open already), and type: E:
7. Type: volumeid E: XXXX-XXXX.
XXXX-XXXX is the new Volume Serial Number that you wish to give to drive E:.
I recommend that you simply change the last character of the original.
Now if you open ACDSee Pro, and perform a search, any file you wish to view full-screen will open without a problem, as it should.