A mod is built as a "unit", all the parts working together. If you then open a saved game from a previous mod, you will likely corrupt the save file and the game both. If you delete game files, you will confuse JSGME and the game. It's very difficult to say where the trouble lays. What you could try, is to de-activate OM and any other mods you have installed, removing them in the reverse order of activation. You could then try to run the JSGME "Compare" utility, if you took a snapshot of the game files before you started installing mods. If not, then you could try
SH Validator, and see what it shows you. If files are not correct (SH Validator will show errors for stock in files that should be ignored), then do a re-install. Backup and then delete your My Documents / SH4 folder to eliminate issues with contamination from it. Activate OM as per instructions in lurker's ReadMe and other files, and see what you get. Just remember, the mod is big, and will need all the help it can get from LAA...