I've had this problem and tried to troubleshoot it for awhile now. Whenever I try to compile to .qc of an exported model i get:
SteamStartup() failed: SteamStartup(0xf,0x0012F170) failed with error 1: failed to take master pipe connection lock
or some variant of the "F170" section of the number, and I get the same error when I try to run TF2 or Source SDK afterward until I restart Steam. I doubt it's the program I'm using, because I have two different frontends that give the same error ( Studio MDL GUI and ConText).
I've gone as far as to reinstall TF2 and Source SDK, but I've noticed that the directory isn't completely deleted so I may have changed a file that's causing this problem.
If anyone knows this error or knows how to check StudioMDL, I would love to find out what I'm doing wrong.