cant join because of map issue

[raidenplays45]

every time i try to join i get all the way to the end and it says that im missing the map but when i look at the download list i have it and every thing with it what do i do

 

[sp00fy]

Try navigating to this location C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\addons and deleting this file: rockford_v2_monolith_1135020244.gma

Then restart Steam, validate your GMod files (Garry's Mod > Properties > Local files > Verify integrity of game files...)
Launch GMod and let it download/install the addon and join the server.

Alternatively, you can download the map seperately and import it directly into your maps folder, but you would need a developer to get a hold of that, as the server uses an altered version of rp_rockford.