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From Autodesk site
"Errors: <ARX file> cannot find a dll or other file that it needs / Unable to load the Modeler DLL's
Published date: 2002-07-26
ID: TS44892
Applies to:
AutoCAD® 2002
AutoCAD® 2000i
AutoCAD® 2000
AutoCAD® 2000 Internet Extension (iX)
AutoCAD LT® 2002
AutoCAD LT® 2000i
AutoCAD LT® 2000
Issue
Error messages are displayed that indicate ARX and DLL files are not loading properly.
Example #1
When starting AutoCAD® 2000 software, warnings are displayed on the command line that DLL files cannot be found when loading the related ARX files:
c:\program files\autocad 2000\acEplotX.arx cannot find a dll or other file that it needs.
c:\program files\autocad 2000\achlnkui.arx cannot find a dll or other file that it needs.
Further errors may occur when trying to load ARX applications that require DLL files.
Example #2
When you invoke a solid model command like SPHERE or BOX, the following error message is displayed:
FATAL ERROR:Unable to load the Modeler DLL's
Solution
These errors occur when the number of characters in the Windows® path and AutoCAD support path gets very large, approximately, over 800 characters. To help avoid this problem, install the product to a location with a shorter path if a large number of support paths are going to be used.
For more information about resolving this issue, see related solutions.
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See also
Error when starting the program: A required .DLL File, AC1st15.dll, was not found"
Bye, and good look
Peth