You cannot open items or reference them in a very deep path in a folder, or when attempting to XREF a file form a deep folder path, you get the notification that path is too long.
This is a limitation of Windows, where the path and the file name and file extension exceed 255 characters. With some Autodesk products, the limitation is about one-half of that (so 127-129 characters), so if you cannot resolve XREF’s (typically PDF’s or Images) or when opening a drawing the XREF’s don’t automatically resolve this may be the cause.
The best solution to this is to try and keep your file directory structure to as few sub-directories as possible and to keep the file names as short as you can, while still making sense.
If in doubt of the length, move the files up a folder or two and see if they resolve (after you fix the paths), if these resolve correctly, then the path to the item (and the filename and extension) are too long and you may need to redo how you have your directory structure at that depth.
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