Thanks Olaf and Tristan for your suggestions. I really appreciate it.
As suggested by Tristan I have modified the vmd_plg.tcl file, and now VMD versions 1.8.6 and 1.8.7 start without error messages.
Also, as I mentioned in my previous email, I have generated some pdb files using the ESPResSo command: writepdbfoldtopo "$ident.vmd[format %04d $j].pdb (Variant 3 in the user's guide section 9.3.2) However, although the command "pbc unwrap" works fine, I still have the problem with pbc wrap (both versions). ----- missing operand at address@hidden in _expression_ "....282137802222821e-8 + address@hidden + *0.0" ----- Any idea or suggestion how to fix this problem? I have attached the first 10 pdb files and vmd_animation.script.