Cannot get included lua functions

I Included a lua file in my fxmanifest.lua. Its supposed to simulate linq functions like in c#. Aside from that I tried two files but the functions in these files just wont exist in my other lua file.

client_scripts { 

I have this in my resource file, but in my menu_client file I get the error “Attempt to call a nil value” when calling a function from the other file.

Can anyone help me?