I don't use EndGraphics and don't have any problems, since graphics are not unloaded from memory as they used to be in previous versions of Blitz (3D, Plus, etc).
EndGraphics does, however, free any graphics you may have loaded. In this case, you will need to reload any media in order to avoid the error you describe.
Also, are you fully up to date with version 1.24 of BlitzMax, as earlier revamped versions of the DX modules have seen some work that could cause errors also. These have now been fixed, so make sure you're fully synced and up to date.
EndGraphics does, however, free any graphics you may have loaded. In this case, you will need to reload any media in order to avoid the error you describe.
Also, are you fully up to date with version 1.24 of BlitzMax, as earlier revamped versions of the DX modules have seen some work that could cause errors also. These have now been fixed, so make sure you're fully synced and up to date.