What is this error? mscorlib_TLB.pas - delphi

Question

We have a lot of Delphi Projects, when I build them before, I didn't see any error. But recently I see the following error when I build one of those projects.
D:\Delphi Projects\MySetting.pas Fatal: Could not compile used unit 'mscorlib_TLB.pas'
At first I thought some background process is using this mscorlib_TLB.pas, then I restart my computer and build it again, it still fails and gives the same error above. What is this mscorlib_TLB.pas error?
Thanks!

Answer 1

You have imported a COM object that is COM Callable Wrapper (CCW) around a managed (.net) object. The imported type _TLB.pas file will (sometimes needlessly) have a reference to mscorlib_TLB in its uses clause.
Delphi's type-library importer is buggy, and there are syntax errors in the auto-generated TLB pas file.
Try removing references to mscorlib_TLB in whatever unit is using it.
If the unit actually depends on something in mscorelib, then you'll have to manually fix the syntax errors in the 400kB pas file.

Answer 2

If you really need to use the library, you can import it using the Component::Import Component tool.

Answer 3

I found mscorlib_TLB alongside a COM wrapper that I built in C# a few years ago, MyComWrapper. When I copied MyComWrapper_TLB to another workstation, it was also necessary to copy mscorlib_TLB since it included type definitions required by MyComWrapper_TLB.
A re-import of the related tlb should regenerate mscorlib_TLB.pas if it can't be found. It appears I reimported the tlb on Oct 4, 2017.
Here's the prologue describing the unit:
unit mscorlib_TLB;
// ************************************************************************ //
// WARNING
// -------
// The types declared in this file were generated from data read from a
// Type Library. If this type library is explicitly or indirectly (via
// another type library referring to this type library) re-imported, or the
// 'Refresh' command of the Type Library Editor activated while editing the
// Type Library, the contents of this file will be regenerated and all
// manual modifications will be lost.
// ************************************************************************ //
// $Rev: 52393 $
// File generated on 10/4/2017 11:15:21 PM from Type Library described below.
// ************************************************************************ //
// Type Lib: C:\Windows\Microsoft.NET\Framework\v2.0.50727\mscorlib.tlb (2)
// LIBID: {BED7F4EA-1A96-11D2-8F08-00A0C9A6186D}
// LCID: 0
// Helpfile:
// HelpString: mscorlib.dll
// DepndLst:
// (1) v2.0 stdole, (C:\Windows\SysWow64\stdole2.tlb)
// Parent TypeLibrary:
// (0) v1.0 MyComWrapper, (C:\source\my-client\client-project\MyComWrapper\bin\x86\Release\MyComWrapper.tlb)