I have couple classing qw teamplay demos. I wanted to merge them together. Unfortunately during playing those demos I have message: Host_error: cl_linkpacketentities: Bad Model Index.

I appreciate some help.

Providing thouse demos may help...

You mean to upload them, how?

How? Upload it somewhere and provide link here.

http://www.ee.pw.edu.pl/~lorenckj/qw3.rar

Played just well with latest ezquake, probably you use some outdated QW client application.

Did you merge all 4 demos together? Did you play it until the end?
If you are positive about that answers tell me exactly how did you do it and which program did you use.
I have another question. When I have a demo, where I want to observe a POV that wasn't originally recorded what happens is that after selecting this POV it automatically changes the person to another one after some time and it doesn't return to this POV. How to fix the POV during demoplaying?

Ah, seems I did not read carefully your first post, I did not merged them, just played each demo separately.