It sounds like you have either a corrupt file or have used a Mod that changes the version number... so I suggest you read the following, especially the part about deleting your Freelancer folder and then re-installing Freelancer...

To play Freelancer in Multiplayer mode on your computer or to host a Freelancer server...
First thing is, you have to have a network card installed in your computer...
Even if you don't have a local area network you still need a network card installed if you want to play Multiplayer...
If you don't have a network card yet they only cost around $20 and are very easy to install in an empty slot on your motherboard.

OK with that said...

First you have to start flserver.exe
(flserver.exe is the program that allows players including yourself to connect to your computer to play multiplayer.)
click on start, then run, and then browse to C:\Program Files\Microsoft Games\Freelancer\EXE
click on flserver.exe then click on open
in the run box you should see "C:\Program Files\Microsoft Games\Freelancer\EXE\flserver.exe"
click on ok
the server configuration screen will pop up
you need to at least fill in the part that says
Enter the name that will identify your server to other players
just put in any name you want such as my server
you don't need to fill in
Enter a description of your server
and you don't have to protect your server with a password
you may want to uncheck the box
Make Your Server Internet Accessible

The first time you do this most likely your firewall is going to ask you if it's ok if Freelancer accesses the internet
if it crashes the first time don't worry just start flserver.exe again.

Ok now you can start Freelancer
click on Multiplayer then LAN and the name you gave your server should show up in the list of servers...
click on the name of your server and then click on connect

Have a blast...

Read this part if you're still having trouble...

Some Mod's need a clean install of Freelancer before you do anything...
Especially if you have used any Mod's before you need to do a clean install of Freelancer.
By clean I mean make sure you get a nice shinny new set of files without any corrupt or files left behind by just doing an uninstall/reinstall. If you just uninstall Freelancer there may be some files left from the modified files (Mod's) in the Freelancer folder. This happens sometimes when you use Mod's...
Don't worry just delete your Freelancer folder this will not cause any problems.
By default your Freelancer game files will be installed and can be located at
C:\Program Files\Microsoft Games\Freelancer

1... Deactivate any Mod's in the Freelancer Mod Manager if you have activated any.
What is the Freelancer Mod Manager? It is a utility made by IGx89 that installs and uninstalls the Mod's automatically in Freelancer.

2... Delete your Freelancer folder located at
C:\Program Files\Microsoft Games\Freelancer
* Delete your Freelancer folder instead of uninstalling Freelancer to make sure there are no files that sometimes can get left behind after an uninstall, unless you check to make sure there are no files left in the Freelancer folders after you do a uninstall...

3... Delete or move any previous saved games... Remove or delete all the files in
Saved games are located in
C:\Documents and Settings\your name\My Documents\My Games\Freelancer\Accts
Both, the Singleplayer and Multiplayer folders.
If you play online Multiplayer the saved characters are saved by the server you play on.
If you don't move or delete your saved games they can cause a conflict and will make Freelancer crash, this is guaranteed!
Why? Because there will be new ships, equipment and other goodies that will not be in your saved game files...

* When you activate a Mod you will need to start a new game.

4... Install Freelancer again with the Freelancer CD.

5... Install the Freelancer QuickFix by Louva-Deus after you re-install Freelancer and before you activate the Mod...
* Some Mod's need the QuickFix installed into your Freelancer folder or they wont work, and it don't hurt to install the QuickFix anyway because it fixes some of the bugs in the original Freelancer files.
* The QuickFix is an exe file...double left click on the file QuickFix-v1.0.exe browse to your Freelancer folder and install the Freelancer QuickFix in that folder.
C:\Program Files\Microsoft Games\Freelancer
* By default the QuickFix installer will select the default Freelancer folder
C:\Program Files\Microsoft Games\Freelancer
You can download the Freelancer QuickFix here.
You can also download the QuickFix from the EOA website at http://eoa.seriouszone.com/?page=quickfix
Freelancer QuickFix is a game patch for Freelancer that 'quickly fixes' a ton of stuff in the game. Here is what is included in the QuickFix package:
* Disables 3D Sound (this caused many problems for people)</dd>
* Enables Advanced Graphics
* Enables Advanced Error Logging
* Updates/Fixes the freelancer.ini file
* Updates the video hardware support
* Freelancer S.D.K. 1.3 (offers over 2000 code fixes)

* Official Freelancer 1.1 Patch (plus version only
The plus version of QuickFix includes the Freelancer 1.1 Patch for those of you who use it. This is provided as a convenience for those who use the official patch so you only need to download one package.

If you want a set of ini files already decompressed into text for editing (making Mod's) you should use the Freelancer SDK v1.3 instead of the QuickFix...
* You can download the Freelancer SDK version 1.3 here.

* If you don't do all the steps above you will probably experience a crash or several other problems.

6... Then activate the Mod using the Freelancer Mod Manager v1.3

7... Have a blast.