Ok, I cleared up the method problem. It lacked the 'static' tag.
No sure what was wrong with the mxml file, but I found out in the end that I didn't need it, so I just removed it from the Library and ... problem solved.
If you had the component in the library at the correct path but you still got that error then you should have checked the library properties and see if that certain component is included into the source. Even though you component in the folder, that doesn't necessary mean that it's included into the final output ( it must be checked in the project properties where the source files are included ).
Yes, you are correct. Thanks for the input.