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

https://discussions.apple.com/thread/1094164