Branch merging

[Prakash Ranade]

It may sound dumb question, even though pls. answer me.

I have branch 2.2 and Main trunk, I have merged branch 2.2 on main and
now all developer have checkout main copy on their module. Now, one
developer who was not aware of this merge process is still working on
branch 2.2 and commits to branch 2.2 for long period of time, How can we
stop his commiting to branch 2.2. Also how can we took his changes and
merge back into main tree.

Any pointers or guidelines will appretiated.

Prakash