I’ve had this problem for a few days now, and I don’t know what’s causing it. The maps in question are rp_city45_2013 and rp_industrial17(all versions).
Granted, I haven’t played either of them in 2 or more years, but I’ve had no problems with other old maps. The progress bar gets to around 50% before dropping me back at the menu.
I found rp_city45 in my subscriptions, only to find out that it was deleted. When I hovered over the link, I saw that the author left a Dropbox link with a VMF http://imgur.com/a/yjJoI. I opened the GMA in my folder and saw that everything except the BSP was still there.
I checked rp_industrial17’s Workshop pages and GMAs, which had all files intact.
I’ve verified the game’s cache and unsubbed from nearly 200 addons that I never used. Someone suggested that I disable all addons and see if they still refused to load, and they did. He also mentioned that if I have too little space, then bigger, more detailed maps might do that. So, I managed to load several large HL2RP maps, and the only other map that didn’t load was rp_rockford, but I’m not worried about that one.
I’d appreciate any help with figuring out why the Industrial17 maps aren’t working. I could understand why City45 wouldn’t work since the map file was gone, but the VMF included the missing BSP and it still won’t load after turning it into a Legacy Addon.