We have seen this problem only twice in two years, both on Windows, but it may be possible on Mac as well.
We have found that some IT configurations lock the typical user's Documents folders on the local machine. One reason we obtained in one case was that the Documents folder was stored in a place accessible from whatever computer the user logs in from, rather than just the local Documents folder.
In any case, SimsUshare uses the Documents folder by default to store sims, but if it cannot write that folder, it sometimes can continue to operate looking like it is working, but any attempt to store pictures (such as when you create a new sim, or try to play a sim), will fail.
One solution is to change the main sim folder, which you can do off of the main screen (New / Edit / Play) from the menu, under the menu item "Change Main Sim Folder". Choose a folder that you know you can write to, for example, create folder on your desktop to hold the sims.
Once you've created the folder and selected it in the operation, now try to create a new sim and load a picture.
If the program still does not work, please contact us
What to Do Next
If this solution solved your problem, you need to talk with your IT administrator to find a folder that you can write to and retrieve files from, safely. Use the "Change Main Sim Folder" method to select that folder.