A: See the following Community Solutions Content:
Author: Prashant Lad, Madhusudhanan Padmanabhan MVP
While installing Visual Studio 2005 Team Foundation Server you get an error that says, “The installer has encountered an unexpected error installing this package. This may indicate a problem with this package. The error code is 26403.”
The error comes up while adding the TFSIdentity user to IIS_WPG group on the application as the machine is unable to contact the domain controller to get the user.
To resolve the issue, you need to add an entry in the hosts file pointing the IP address of the domain controller against the domain address.
To add an entry in the hosts file
Before you run the installer again, make sure to do the following:
Applicability: Visual Studio 2005 Beta 1 Refresh with Visual Studio 2005 Team System