You may have installed the library files, but when you opened up VB6, it loads the components; If the component is not found, it’ll stop the load and tell you there was an error, if you continue to load, it will remove all instances of that component control from VB6.
What you’ll have to do is click (Project > Components), select (Microsoft Rich Textbox Control)
Then go to frmMain, in your Toolbar, you’ll have a symbol like this:
Click that, drag your mouse over a place in frmMain to make the Rich Textbox control:
Go to the properties window (Bottom Right corner of VB6)
Rename it to txtChat
Then your code will work.