I am able to login in my PLM instance , but not able to connect YPLM plugin 5.2.1
If you are able to login to YuniquePLM without issue, but are getting "incorrect login or password" message when logging into the Design Suite Plugin in Illustrator, then you'll want to check settings in the plugin and YuniquePLM Administration.
If you are the administrator:
Let us know if this helps!!