hi,
with your build installed the error is strange, if you've already done all the checks suggested by the blogs and it happens only to users with restricted access to the internet.
That bug on the control of the classic client build has been fixed by build 28981 - kb n. 969448
Update 0.13 28981 969448 Error message when you open a report in the Microsoft Dynamics NAV Role Tailored Client that does not have a report definition layout in Microsoft Dynamics NAV 2009: “Microsoft Dynamics NAV Classic client is opened from an untrustworthy component”
www.waldo.be/.../platform-updates-overview-nav2009
Microsoft Kb
mbs2.microsoft.com/.../KBDisplay.aspx
Try to post the case on the Nav official team blog, maybe there is some other fix is not published
blogs.msdn.com/.../where-does-rtc-find-the-classic-client-for-running-classic-reports.aspx