All SOLIDWORKS Toolbox parts have an internal file flag that sets them apart from regular SOLIDWORKS parts. This flag enables SolidWorks to recognize them as standard parts and places a Toolbox icon beside them in the FeatureManager Design Tree. If you have created custom fasteners by copying files out of the Toolbox folders, these will still be recognized as a Toolbox part. As these are now stand-alone parts, SolidWorks will not need to search for the references within the Toolbox. Therefore you should remove the internal flag to avoid file reference conflicts.
- Browse to your SOLIDWORKS installation folder (by default C:\Program Files\SolidWorks Corp\SolidWorks)
- Within the installation folder, browse to Toolbox\data utilities
- Run sldsetdocprop.exe
- Add custom fastener files, set the Property State to No and click Apply