I would suspect a server timeout memory issue trying to process all those preview images. what is your php memory set to? There are tutorials here on using ini_set to raise php memory that may help that issue.
The lang search is built to return all results LIKE what you type not an exact result. It is case sensitive though.
am I right to say your searching for Fri versus fri? I am not sure there are any phrases like that in our default code.
I can do an example here. If I search for upl I return 4 pages of results any string with upload in it thats correct. If I type Upl I get one page of results which are all strings with Upload in it.