Try resubbing and see if it works, sometimes the workshop likes to be grumpy.
Make sure you exit Black Mesa too.

If the above doesn't work, you can try a little more troublesome way:
Go to steamapps\workshop\content\362890\822401059\

and open the .vpks with GCFScape,
http://nemesis.thewavelength.net/?p=26

and drop them into your common\black mesa\bms\
folder.
You shouldn't have to do that, but that's the way you can be sure the maps will load.
You may have to do the same with the resource pack. You shouldn't need to, but ya know.. Grumpy workshop.