I know what you mean, phox. One does feel 'lonely' sometimes about reporting weird errors. I wonder -- just guessing -- if this one could have anything to do with Vista permissions for the SYSTEM user, and/or perhaps the file types (non)association issue. I also get a similar error if I try to open a local HTML file in IE. I hope Nightman and 2aCD don't give up on it entirely.
Anyhow, all things considered, VistaPE's few 'rough edges' aren't too bad at all. With a few minor mods to the Grub4Dos part of the Standard-7-iso.script, I've actually got it working with WinBuilder's BartPEcore output to create an 'all-in-one' DVD. Just as another example of how easily minor oversights can cause major problems, I almost missed BartPE's lower case file name output (setupldr.bin and s_setupldr.bin) which Grub4Dos (*nix) doesn't recognize as the correct files for booting into the on-CD and in-RAM options.
One minor feature that I really do miss in VistaPE is a Command Prompt Here item in the context menus. NightMan might want to consider adding it to the main package -- just two registry lines:
RegAddBoot,"HKLM",0x1,"SOFTWARE\Classes\Drive\shell\Command Prompt Here\command","","cmd.exe /s /k pushd ""%V"""
RegAddBoot,"HKLM",0x1,"SOFTWARE\Classes\Directory\shell\Command Prompt Here\command","","cmd.exe /s /k pushd ""%V"""