If you see messages like this when you attempt to play a mission, chances are that this is being caused because you are missing an addon that the mission you're trying to play references.
This message can also be issued when OFP starts up and an existing addon is dependent on another addon that itself is missing.
In this case, if you're not sure which addon file is referencing the missing addon, simply use Windows File Finder utility. Click on the Windows START button, choose FIND and then FILES OR FOLDERS. Leave the NAMED field blank and fill in the CONTAINING TEXT field with the name of the addon appearing in OFP's error message. Click the BROWSE button and select OFP's ADDONS subdirectory or OFP's base directory for a longer, more thorough search. Check the INCLUDE SUBFOLDERS option and click FIND NOW to begin searching.
If that's not it, maybe it's because you installed a version patch without that version's addon components. That option was available for several of OFP's upgrades. An easy way to check this is to look at the size of your patch files and compare them to the size of the Ultimate Upgrade patch files listed on BIS' download page. If the size of any of the patches you installed is relevantly smaller than the size of the same version's Ultimate Upgrade patch file, you've most likely installed a patch file rendition that just updated OFP's code but did not include that version's addon files.
In these cases, the solution is to either install the addon(s) or forget about playing the missions that require them.