People using Macs have reported strange folder names which can have a mixture of numbers, letters, foreign language characters, and + symbols, such as this:
QoMmwjzVS7+3ZqFsSk&0HQ (1)
A fix reported in the Picasa forum is as follows:
1) In Picasa, go to "File" > "Add folder to Picasa" (or "Tools" > "Folder Manager")
2) Go to Mac HDD / Users / YourName / Pictures / Photos Library / Masters
It is probably marked with the blue circle icon for "Scan Always"
3) Click "Remove from Picasa" then select OK
4) Go back to the same Masters folder and select "Scan Always"
While on Step 4, change these folders to "Remove from Picasa":
Mac HDD / Users / YourName / Pictures / Photos Library / Thumbnails
Mac HDD / Users / YourName / Pictures / Photos Library / Resources
Mac HDD / Users / YourName / Pictures / Photos Library / Previews
Another option is to navigate (through Finder) and rename the entire Photos Library folder in "Pictures." See if that resolves the problem. If not, you at least have the renamed folder as a backup should you wish to revert back to that folder.
Reference links from the Picasa forum:
https://productforums.google.com/forum/#!topic/picasa/sNBXwDUmOYM
https://productforums.google.com/forum/#!topic/picasa/H5t42vrzG0U
https://productforums.google.com/forum/?hl=en#!topic/picasa/cHHNWJZVFj8
https://productforums.google.com/forum/#!msg/picasa/sNBXwDUmOYM/tT7GvRDOWc4J
More info:
http://apple.stackexchange.com/questions/156590/weird-folder-names-in-library-preferences