This is probably just a case of standard growing pains, as the red-hot Turntable.fm group listening service tries to keep up with demand, but hordes of users are reporting being denied entry to the group listening service on this lovely Friday morning.

Update 4:12pm ET: Turntable.fm says it has fixed the problem, which it called a “database issue,” and asks users who continue to experience issues to respond on Twitter.

The site denied access to all IP addresses outside the United States earlier this month, but today’s partial outage appears to affect U.S. users.

“Twitter is loading really slow and @turntablefm isn’t letting me log in. The Internets are broken,” laments jnette in one of many complaints about the lockout on Twitter.

Evolver.fm has asked Turntable.fm what’s going on here, and we will post an update if we hear back (see update above). So far, Billy Chasen and company are not talking. From what we hear, the lockout is due to some sort of “database maintenance.”

We aren’t too surprised by the outage — after all, when we first wrote about Turntable.fm, we charted one potential path for the service:

Big splash –> Performance issues –> Get sued –> Go under/get bought –> Be lame

Have we entered phase two of this ignoble process? Only time will tell.

If you find yourself locked out of Turntable.fm this morning, perhaps give one of these alternatives a whirl — although none of them have the buzz, avatars, or game mechanics that have made Turntable.fm such a hit among music nerds.

Pro tip from our pal John Brownlee: “[The block appears to be] IP based. If I log in with my iPad on 3G, it works fine. Not fine on my home network.” It sounds like Turntable.fm is turning some users down based on their IP address; switching to the coffee shop, a tethered smartphone, or some other location might let you back in, if you’re blocked.