Files created and saved in SOLIDWORKS Connected Makers version are embedded with a watermark. This information is made available on 3DEXPERIENCE SOLIDWORKS for Makers website as well. 

“Are my files or data restricted at all?

Files and data created with your Maker account are digitally watermarked and can only be opened up in another Maker platform. You cannot open up files created with your Maker account within a commercial or academic platform. This digital watermark is added to native 3D file formats, such as .3dxml, .sldprt, .sldasm, and .slddrw. Neutral 3D file formats, such as .stp or .iges can be opened on any platform.”

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This error is also seen in some cases where users might have access to Makers platform as well as a commercial 3DEXPERIENCE platform. 

If the file in consideration was created/saved with the SOLIDWORKS Connected for Makers application, it can only be accessed (opened) via SOLIDWORKS Connected for Makers. The above error is seen if the user launches SOLIDWORKS Connected application via commercial platform. 

In this case, follow these steps to open the file in SOLIDWORKS Connected for Makers. 
1. Close all the SOLIDWORKS sessions.
2. Log out of the 3DEXPERIENCE platform, where you are currently logged in and have launched SOLIDWORKS Connected.
3. Clear browser data, close and restart browser. 
  Note: Recommended browsers are Google Chrome, Mozilla Firefox and Microsoft Edge.
4. Login to Makers platform​​​​​​​. 
5. Once logged in, navigate to My Compass > My Apps > click on SOLIDWORKS Connected to launch the application. 
6. Make sure that after launching SOLIDWORKS, it shows SOLIDWORKS Makers on the home page.
7. Now, open the files created in the Maker's version. The file should open now without an error.