Hello Erik,
WPM creates accounts during start of the service "SolarWinds WPM Player". You can find a log for this service in "c:\ProgramData\SolarWinds\Logs\SEUM\AgentService.log". Check if the service is running under Local System account. If not, change service details to use Local System which should give it all required permissions.
In theory you can create those accounts manually. They should be named "SEUM-User-#" where # is a number from 1 to 7. They should be part of local "Users" group, user "SEUM-User-1" should be also part of "Remote Desktop Users" group. You should also create a group called "SolarWinds-SEUM-Users" and assign all those accounts to this group in addition to Users group.
However, even if you create accounts manually it may not help. It seems that service has issues with permissions so even if it starts, it may not be able to work correctly. I recommend looking at service log what are the errors related to user account creation. There should be some error code why accounts creation failed. You can check what that error code means for example here: System Error Codes (Windows)