Terminater 2 Soldering

Ok, so I'm cruising along, sweating joints and I'm down to my second to last one. Everything is good, I've got everything set, copper shined up, flux added, pipe & T fit together, adjacent joints have a damp cloth wrapped around so they don't come undone.

I heat up the T (coupling) and instead of a nice flow of solder in the fitting, the solder cracks apart and falls off, a bit melts, but just on the pipe.

What gives? Any help would be appreciated!

I don't know I'm not there!
Cleaned?
Fluxed?
is the pipe open To allow the pressure out IE valve or faucet open?
Any water in the pipe?

Sounds like water in the pipe to me. Even if it is some distance away, when you heat the pipe, it heats that water and you have water vapor. You were OK when the pipe was open to vent the vapor, but with the last fitting in place, it will come through the space between the fitting and pipe.

3rd time's a charm - got it to work

Not sure why it didn't the first two times - definitely no water in the pipes, I'm getting things ready before I hook up to the source. I have openings so that wasn't an issue.