Greetings,
Yes, editor upgrades do conflict with each other. To get the missions to work again, try:
You have two editor upgrades installed, 102 and 111 (or something similar). Find the newest one (111 - the one which you installed most recently) and change the file extention from .pbo to .pbx (or something different). Then OFP will stop recognising it as an addon, untill you rename it back to .pbo.
Remember to rename it correctly after you have finished playing the old missions. Note that you will have to restart your PC [EDIT: Mental Abberation, sorry. Just restart OFP] every time you remove/ add a new addon. Only ever have one editorUpgrade active at any one time.
And now the editing stuff:
Kegetys advice to reopen old missions in the editor and then resave them is intended mostly for the creators of the original missions. If you have created any missions using the first EditorUpgrade, then this is the course of action for you to follow.
-Supr. Cmdr. PsyWarrior
-Psychic Productions