SquirrelMail version 1.4.4
The problem occurs if you use the preference database
(instead of files) and users have folders / subfolders
longer than 64 characters.
In this case collapsing a folder in Squirrelmail will
lead to the following error message:
Preference database error (unknown error). Exiting
This is caused by the prefkey field in the database
being only 64 characters long. In the case described
above, Squirrelmail tries to insert into the prefkey
field a longer value (collapse_folder_<folderList>).