The 1.6 Admin installation installs the GroupWise trusted application DLL ‘GWTApp.dll’ to the client location.
Currently, there is no switch available in the Admin installation that stops the installer from attempting to install this file. (This is the first report we have received of this being a problem).
Accordingly, the only way to work around this problem at the moment would be to temporarily grant yourself write access to the shared client folder, install Admin, then remove write access. Alternatively, you might be able to manually copy the trusted application DLL to the shared location, then try installing. The installer will probably not attempt to update the file in this scenario. I could organize to send a copy of the file is you wanted to try this.