Using a Dropbox folder is a great way to share your ProSelect setup data between your ProSelect installed computers (using the "shared folder" option) and it can be used for sharing ProSelect album files between computers provided you do not open your album files while they are in a Dropbox folder.

When you have a ProSelect album open, ProSelect is usually doing regular updates to the file. These updates include:

1. Locking and unlocking the file to prevent accidental access from two different user at the same time,
2. Storing periodic auto-backups. 
3. Adding extra images when you import them into the album file.

Dropbox assumes that files in a dropbox folder are not constantly being updated so, if you have an open album file in a Dropbox folder, Dropbox will attempt to copy/sync the album file between the "cloud" and your other computers each time a small change is made. This can result in Dropbox getting confused and making lots of different copies of the file or worst case corrupting the .psa file itself and you loosing all your album data.

Also, because a ProSelect Album is a database, a journal file is also temporally (for a fraction of a second) created along side the album file whenever any changes are saved which may further confuse Dropbox and this file is certainly one that you don't want to be copied between computers.

On top of this, because Dropbox uses the internet to synch data between computers there is always a delay before the files are fully transferred. This can allow two or more users to have the same ProSelect album file open at the same time and this can result in data loss or album file corruption.

Finally, what will really mess things up is that some Dropbox accounts will allow you to select to keep all your files "in the cloud" to save space on your disk. Doing this will cause unknown errors in ProSelect because it relies on any files being instantly accessible from a local location.

If you wish to share .psa album files between users on the same local network, it is best to use a shared folder on one of your computers instead.

If you wish to shares album file between computers not connected to the local network, you should only transfer them by copying them into and out of your Dropbox folder while they are not being used by ProSelect.

For more on sharing data, please see "Sharing Data between Computers" & "Using a Shared Folder" section in the ProSelect Reference Manual (quick access under the Help menu in ProSelect). There is also a helpful article Sharing Data between computers.

We recommend backing up your data periodically and this applies to doing so prior to setting up your data sharing options in ProSelect. You will find helpful information in "Backing up and Recovering your ProSelect Setup Data" section in the ProSelect Reference Manual. And the article Transferring Prices and Templates to another computer also has how to do this.