This fatal error occurs when the declaration of symbol declared in the interface part of a unit has changed, and the compiler cannot recompile a unit that relies on this declaration because the source is not available to it.
There are several possible solutions - recompile Unit1 (assuming you have the source code available), use an older version of Unit2 or change Unit2, or get a new version of Unit1 from whoever has the source code.
This error can also occur when a unit in your project has the same name as a standard Delphi unit.
For example, this may occur is when compiling a project written in a previous version of Delphi that did not have a unit of this name (for example, search.pas was not in Delphi 3).
To solve the problem in this case:
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