We also have some users with this issue.
Hear are my 2 most common solutions for this problem. Some I don't advise you to yourself if you don't have the experience in windows.
In that case I would recommend your Reseller or ict to perform the solutions
restore your file association of the .sldprt, sldasm, slddrw to the Solidworks launcher
Reset the following registry key to blank ( I recommend you ask your ict or reseller to do this( it can cause damage to your system if not done properly)
I hope this helps
with kind regards
Thanks, it took a combination of the two. I had tried the files association before to no avail. When I edited the registration key as described and then went back and redid the file association to the Launcher it seems to be holding and not opening simultaneous sessions.