I think there is an easy solution to this.
1. Right-Click on "joint group" and click edit beam joints.
2. There should apprear small spheres on the model, Golden puke-yellow for the end of a beam, and pink for a beam joint.
3. right-click on the golden coloured "end" joint that you want to be welded to the bigger wide flange beam.
4. A little dialog window pops up showing (you already knew this) that the only beam involved in this joint is the single beam.
5. Click on the other beam to which it's supposed to be welded. Now two beams should appear in the little dialog box.
6. Click "calculate" in the beam joints property manager window. The golden joint should change into a pink "joint" and all should be well.
If the steps I've described don't work, you can read more in the simulation help file under "beam joint".
Thanks for the tip David, your suggestion worked for most of the joints, although there was still some odd behaviour with some of the joints for no apparent reason.
dear david.thanks for your answer. i have same problem and solve with your solution steps.