You say that there were no changes made that could cause this problem.  What changes have you made recently?  The problem you are having is that there is a control called the pager that cannot be loaded anymore.

The only reason that could happen is if the file was deleted, read permissions on the directory had changed or you upgraded versions of DNN and the Gallery can't call the version it needs.  The control name in the .aspx file might have been changed also. 

i face the same problem,and i checked the log and it show the same problem,and the problem in the Page_load functions.

By the way,my folder has read/write permission,i don't know from where this error is raised ????????!!!!!

any help,since i removed my gallery form my portal bacause of this critical error.

i tried to add gallery in  a new page,and i got the same error,this means the problem in the gallery module itself.

i'm running 4.3.x version of DNN.

Thanks in advance.

The right answer, exact way to fix.  Well, that is simple.  Uninstall the module and find an alternative.

Sorry, but the currently released Gallery module has a bunch of known issues and there is no easy fix.  There is a patched version at www.Jegers.com that has MANY bugs fixed in it, and if you want to start from there and then post questions, there is a better chance that someone will actually be able to fix something.