In OFP: Resistance, a mission that references addons, must contains an ADDONS section, listing all of the addons used by the mission.
In earlier OFP versions, using OFP's mission editor, addons were automatically added into the ADDONS section whenever an object or a unit from any addon was inserted using the mission editor. However, there were two cases in which an addon object's or unit's name was not automatically inserted into the ADDONS section by the mission editor:
The result of the above circumstances in older OFP versions was to frustrate a lot of players who downloaded missions that required addons that the players didn't have. When attempting to play such mission, older OFP versions did nothing but display vague and cryptic error messages about a missing addon.
OFP: Resistance has been improved in this regard, as follows:
By introducing the above changes in OFP: Resistance, players can now more easily detect if they have all necessary addons to run a mission and, if not, they'll know the names of the addons that are missing.
Many missions that worked without problems until now will cease to work properly. SP missions will display error messages and MP missions will not run at all.
Note for Server Host Administrators
Server administrators need to guarantee that the missions they use have all the required addons listed in their ADDONS section. For most missions, simply opening the mission in the mission editor, previewing it and saving it again should automatically update the ADDONS section list with all the referenced addon names.