Yes, post your log file as The E said. What you'd be looking for is, say, either another derelict folder under the original one, or perhaps a derelictSCP folder etc. Some zip files are packaged differently (some have the derelict folder included, in which case you would extract the file including the folder structure into \FreeSpace2\, and some do not, in which case you would make a folder called derelict, and then extract the file and folder structure there.)
Just check any folders you find that are underneath the main derelict folder, and be sure you don't find any .vp files there, as they go in the main derelict folder.
post your log file, and we will be able to see exactly what your folder structure is, along with other useful troubleshooting information.
Just so you know, a .vp file is a
Volition Package file. It has folders inside of it, like a .zip file.
So, your actual folders would be, say, \FreeSpace2\derelict\data\tables, but, the \data\tables is inside of one of the .vp files so as not to make a big mess of the mod folder, and to make additions (mods) easy to find, because, anything that is
actually in the folders will be use instead of the file inside the .vp if there is more than one copy.
So, you could, say, replace a model of a ship if a new one was released before the next version of the mod came out by placing the model file into the folder \FreeSpace2\<mod name>\data\models\<new_model_name>.pof, and this would replace the .pof file found in the .vp file which had the \data\models directory.
How does this (possibly) affect your situation?
Well, if you had \FreeSpace2\derelict\derelict\derelict.vp, and you select the \FreeSpace2\derelict mod folder, then the game looks for the required files in \data\ and the other correct folders, under \derelict\, whether from inside a .vp or an actual file in the correct paths, and if those files are under another folder, it will not find them (such as possibly the campaign file?

).
However, lesson over,
post your log file. That will tell us what we need to know,
including your files/folders. I should have asked you to post it along with my suggestion, but I was taking a quick stab in the dark in case that (extracting to extra subfolders) was your issue. Sorry!

@The E, if they have the correct files in a subfolder, the .log file shows it, right? Or does it only show what the game scans for content?