Lazarus: Can't find unit [unit] used by [program]

I'm trying to use an external library (wingraph)开发者_如何学编程 in a simple program. I have .o and .ppu files. I added the directory that contains them to the list of both "Other Unit Files" and "Include Files" paths under Project->Compiler Options. When building, I still get the error "Can't find unit wingraph used by [program]".

The library is Windows specific and I'm compiling on Windows, too.

What should I do to solve the problem?

Note that I don't have extensive knowledge about Pascal itself nor its tools. I'm just trying to quickly help someone start using the library.

It was the problem of outdated compiler

In future, if this happens make sure any Units used in main units are tagged in the 'uses' section as such:

uses Unit1, Unit2...;