I need your help.   With regard to the subject heading....

AFAIK declarations like

program A;

uses B;

type
  PInt = ^Integer;

var
  IntP : PInt;

   Proc( IntP); { here you'll get type mismatch }

.....

unit B;

interface

type
  PInt = ^Integer;

  procedure Proc( IntPtr : PInt);

can cause this problem. Do not declare the same type in two places
even the declarations are the same.
If it's not the reason - you can email me your code, or better just
post a new article with some code (not too much).