Have you tried to reinstall EPiServer Manager 1.1? (uninstall the current version, then install it again) There was a problem with the first build of EPiServer Manager 1.1; an updated version of the EPiServer.Install assembly, that was included with the EPiServer Manager 1.1, had accidentally the same version number as the EPiServer.Install assembly that was included with the EPiServer Manager 1.0. So, when EPiServer Manager 1.1 was installed over the old 1.0 version, the new EPiServer.Install assembly was not installed correctly. Uninstall/reinstall of EPiServer Manager 1.1 fixes the problem. I suspect you have this problem, the "not marked as serializable" error sounds familiar ;-) ... I might add that the current build of EPiServer Manager 1.1, that can be downloaded from episerver.com today, has been fixed and does no longer have the issue above (it was fixed the next day after the 1.1 release). EPiServer 4.51 is currently being tested. If everything goes as planned, it will be released 23 September.

This problem will need a hotfix to be solved. Please contact support in order to receive the appropriate files.