Thank you @Carl Love 

My english can sometimes be a bit ambiguous. The procedure i sent was just to encapsulate my problem and is not the procedure i am working on. Is there a solution such that my argument g or your argument f could be an expression as x^2 without having to predefine this expression as a function. 

As example

When i plot y=x^2 i can write "plot(x^2);" as well as "f(x):=x^2;plot(f(x);" 

and is there a problem with this?; "Your first line includes the parameter declaration var:= x. This makes var the parameter, and its default value will be x if SomeProc is called with less than two arguments."

Thank you 

@John Fredsted 

The command worked but the real problem was that I did not run my the document as an administrator. Propably a rookie mistake.

@Mac Dude 

 I have done as adviced. When I in the worksheet below my "package" execute:

LibraryTools:-Save(MineRedskaber, cat("/Program Files/Maple 2017/lib"[1], "/MineRedskaber.mla"));

Where "MineRedskaber" is the name of the module and file (It's danish). Maple returns the error message:

Error, (in LibraryTools:-Save) could not open `//MineRedskaber.mla\MineRedskaber.m` for writing