sometimes that happens if you are running solidworks in non administrator account. solidworks can not obtain write access to users folder. you can try to right click on solidworks icon and run solidworks as administrator. if that wouldn't work try to save files in different location outside users folder.
I set SolidWorks to open as administrator but received the same massage.
Can you tell me where to set the default working folders? I can't find any option settings that identify folder management for saving local copies of downloads from our server or in this case, where C:\Users\Peter\Documents\ is set for FloXpress.
what operating system are you using? what variant of the operating system?
what level of UAC is enabled?
I appreciate that this was posted a long time ago and I expect you have found the solution; for the benefit of future users with this problem, I have just discovered that taking ownership of the model overcame this error message.