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.

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It was the problem of outdated compiler

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

uses Unit1, Unit2...;