ok,
Seems like your going to need to change the version of FLserver.
You see you got your FL.exe and FLserver, they are both 1.0 (as they should be in normal FL.)
Now what some mods have is just change the version of their EXE file. This is easy, but...I am not sure I am allowed to talk about it(becuase big bad microsoft might make a flood to wash us away.), but here we go. (don't forget your life vest)

Ok the frist program your going to need is called ResHack(look it up on yahoo or somewhere), it's a program that messes with complex files that shouldn't be touched in this game.
Anyway, once you get the program, open it up, k? Now since I am already guessing the mod changes the version of the game, all you going to need to do is change the version of FLserver.
Find FLserver and make a backup of it and go to file and open up FLserver. You'll see [Icon , icon group , Version info

Now I am already sure you know where we are going. Yes, the version info.
Now when you open this up you'll see a folder called 1 and then a gear called 0. Click on the 0, On the right you'll see a ton of words, numbers, etc. WHOA!
As you can see that's a lot of stuff for a person to take in. But if you look at your normal FLserver by just hovering your mouse over FLserver, you'll see the product version. TA DA!

1 VERSIONINFO
FILEVERSION 1,0,1223,11 <----change 3,1,1223,11
PRODUCTVERSION 1,0,1223,11 <---- change 3,1,1223,11
FILEOS 0x40004
FILETYPE 0x2
{
BLOCK "StringFileInfo"
{
BLOCK "040904b0"
{
VALUE "Comments", ""
VALUE "CompanyName", "Microsoft Corporation"
VALUE "FileDescription", "Freelancer"
VALUE "FileVersion", "3, 1, 0, 0" <--- change
VALUE "InternalName", ""
VALUE "LegalCopyright", "© 2003 Microsoft Corporation. All rights reserved."
VALUE "LegalTrademarks", ""
VALUE "OriginalFilename", ""
VALUE "PrivateBuild", "Release"
VALUE "ProductName", "Freelancer"
VALUE "ProductVersion", "3, 1, 0, 0" <---- change
VALUE "SpecialBuild", ""

Anyway right above the screen you'll see a button called "Compile Script", click that bad boy and then save. IF you did everything right, the file version when you hover your mouse should say 3,1,1223 bah bah bah. Then when you enter the game it should look like this.



So like I said above, if this counts as hacking the untouchible file, then Admins, you may remove this post.

QuEsTiOn AsKeR
Last Hope MOD

Some of the mods have a modified flserver.exe file that changes the version so you would need to have that flserver.exe file.
This is done so that you have to play on their server.
After all someone did all the work and spend countless hours making the mod so they are entitled to limit its use if they want.
Fortunately most of the mods do not have a modified flserver.exe file so everyone can use that mod, weather it's on your own computer in a multiplayer game or to use the mod on an online server.