Previous versions of VBLM relied on project file extensions almost exclusively to classify project files by type (frm=form, cls=class, etc), and generally treated all non-standard extensions as modules.
I recently discovered that the VB docs are wrong when they say that all post-VB3 file types must be named using the standard extensions; you can indeed use other extensions, and VB will usually figure out the correct file type. Previous versions of VBLM, however, did not, which could cause problems if it misinterpreted a type.
As of V5, the first time VBLM encounters a non-standard file extension in a project -- that is, any extension other than the official Microsoft VB file extensions -- it is going to stop, display it, and ask you a) to confirm the file type it indicates, and b) whether or not the extension ALWAYS indicates this file type, ie is "associated" with it. If you answer Yes, VBLM will store the association in VBLM.INI, and will not ask about this extension again. Over time, VBLM will thus build a list of all the extensions you use and the file types they indicate.