Error opening mapname
Error opening mapname.bsp
The compiler can't find the *.bsp file of your map or it's corrupted. Your .bsp file was probably not created in the first place due to an error during the vbsp stage of compiling. If not, check the pathname. With Hammer 4 and its auto-configuration settings, you generally do not need to worry about the copying procedures in the configurations. Another common source of this problem is spaces in your map name - rename your map file or do a save as with a different name with no spaces.