Busy signal error 0xC00A000E on callback fix

If you're staring at 0xC00A000E after configuring callback on Windows Remote Access Service, I've been there too. It's annoying because everything looks right but the connection fails when the remote site tries to call you back. Here's the fix — skip the fluff.

First thing: disable callback

The fastest solution is to turn off callback entirely on the client side. Open the modem or VPN connection properties. For a standard dial-up connection:

1. Go to Control Panel > Network and Sharing Center > Change adapter settings.
2. Right-click your connection > Properties > Securiy tab (or Networking tab, depending on Windows version).
3. Look for "Callback" — set it to "No callback" or uncheck "Require callback".
4. Click OK and try connecting again.

If you're using Routing and Remote Access on a server, check the user properties under Active Directory or local SAM. Open rasphone.pbk if needed and remove the Callback= line.

Why this works

What's actually happening here is that Windows expects the remote modem to call back at a specific time. If the remote line is busy — maybe another call, or the modem is still negotiating — the local modem hears a busy signal and throws 0xC00A000E. Disabling callback means the connection happens immediately without waiting for a return call. The remote modem just picks up and authenticates. No busy, no timeout.

The reason step 3 works is that Windows stores callback settings per connection profile. If you're on a corporate VPN, the server-side policy might override your local setting — but most home setups don't have that.

Less common variations

Modem timeout too short

If you really need callback (security policy, maybe), increase the timeout. The default is 60 seconds. Some modems take longer to hang up and redial. Open the modem properties in Device Manager:

Control Panel > Hardware and Sound > Devices and Printers
Right-click your modem > Properties > Modem tab
Set "Maximum Port Speed" to 115200
Check "Enable modem speaker" to hear the busy — helps debugging

Then in the connection's properties, go to the "Options" tab. Increase "Redial attempts" and "Time between redial attempts". I bump it to 120 seconds between attempts. This gives the remote modem time to finish its previous call.

Phone line noise or wrong dial prefix

Sometimes the remote site's modem picks up a second line that's actually busy, not the callback line. Check the dial string in the connection properties — if you're using a prefix like 9, for an outside line, make sure it's correct. A trailing comma adds a pause. Test by dialing the remote number manually from a phone — if you hear a busy tone, the problem isn't Windows, it's the phone line.

RAS server callback policy

On a Windows Server running Routing and Remote Access, callback settings can be per-user in Active Directory. Open Active Directory Users and Computers, find the user, right-click > Properties > Dial-in tab. Under "Callback Options", pick "No Callback" or "Set by Caller" (timeout issues). If set to "Always Callback To" with a number that's busy, you get this error.

Prevention for next time

Callback is a legacy feature from when phone lines were metered and you wanted to reverse charges. These days, it causes more problems than it solves. If you don't need it, disable it permanently. If you do, test the callback number from a regular phone first. Also set the modem timeout to at least 120 seconds on both ends. And if you're using a DSL modem or cable modem, callback doesn't work at all — those aren't real analog modems.

One last thing: update your modem driver. I've seen old Conexant drivers (Windows 7 era) that ignore timeout settings and always fail after 30 seconds. Grab the latest driver from the manufacturer's site, not Windows Update. That alone fixed 0xC00A000E for a guy I helped last month.