When we upgraded to SW 2017 last summer, our .dll macros would sometimes quit working. No obvious reason. Occurred on 8+ cad stations.   Our .swb macros still work consistently. This is an intermittent problem. Sometimes closing down SW and restarting it will fix the issue. Sometimes not.  Sometimes rebooting the entire machine will fix it, sometimes not. Seems to be a simple path problem.

Error message is:

Cannot open M:\Design\Mechanical\Solidworks Data\Support\Macros\vb.NET MACROS\Partnumber2\SwMacro\bin\PartNumber2.dll

I go to the directory and that file is there.