If you are unable to load a PostScript file, check the beginning of the file (uncompressed if necessary). The file might not be a PostScript one or it may have been created on a system that uses a different character for line ending than Unix (e.g. a Mac). The simplest solution for the latter is to make a small perl script that converts the file into the correct format.
If you get a dialog popup when you load or view a PDF document, whose title bar mentions gs warnings, this could be for several different reasons. Please note, however, that the problem is not with GGv but with Ghostscript, which GGv uses to read the files. The first reason might be that the document is encrypted, and you are using a version of Ghostscript which does not support encryption due to legal issues. To fix this, you must find a modified version of Ghostscript that supports encryption. The second reason might be that the document uses new PDF features that haven't made it to Ghostscript yet. In that case, you can upgrade Ghostscript if there is a new version available, or simply report the bug to your vendor.