I can't say that this always occurs, but often if I try to export a map, then click cancel for whatever reason, jDip will do nothing if I attempt to export the map again. After clicking Export Map>JPEG/PNG/etc. jDip does nothing. The only way I've found to remedy this is to close jDip and open it again. This may be isolated to either v1.6.8 or v1.7.0; I use both versions. I'll report back when I've done a bit more testing.