So our company recently switched to a consolidated MRN license from site specific licenses.  Soon after we switched, we found that many of our Solidworks users would get a message after launching Solidworks:

"Unable to obtain a license for the following product(s):

SOLIDWORKS Workgroup PDM

You will be prompted to save any modified documents."

The user would then have most of their functions grayed out and if they had files open they wouldn't be able to save them, but would have to perform a save-as.  Many of our locations currently have Workgroup PDM, although we are moving to a centralized EPDM system.  We have a lot of SW Professional licenses, and about 4 Workgroup PDM licenses for users without Solidworks or with Solidworks Standard.

By examining the license server log file, we found that users would get these errors when the 4 Workgroup PDM licenses were all being used, it would try 4 times to get a Workgroup PDM license, fail to do so, and not pull a Professional license, even though we had many available.  At first we thought this was an issue with the license order and tried correcting the user's license order.  It seemed like in some cases this worked but in most cases the problem persisted. Eventually submitted a ticket to one of our resellers, but did not get much information back from that.  Finally I determined that this error is caused because unlike with any other Pro/Prem Add-in, Workgroup PDM add-in will not automatically pull a Pro or Premium license if NO other Pro or Prem add-ins are enabled.  It will simply try to get a pdmworks license and if none are available, it will fail and lock the user out of PDM functions.  The workaround is to enable any other Pro or Premium add-in like Toolbox or Utilities or Photoview.  I confirmed this with my reseller who confirmed it with Solidworks, but Solidworks says this is working as intended and doesn't feel it's a bug.  In my opinion, this IS a bug and Workgroup PDM, being an add-in which normally requires a Pro or Premium license, should grab one automatically if no pdmworks licenses are available.  Our users shouldn't have to enable and load add-ins they do not use or need just to get PDM Workgroup to work properly. I wanted to post this as a heads up because I could not find any other information on this in the KB or the forums, in case anyone else runs into this issue.