Messagebox is properly identified using Record Identifiers, but is not found when running a script. The Tag is: "~ActiveApp/[DialogBox]$MessageBox". I have tried WaitToExist, but it is not a timing issue, but rather an identification issue. If I create a new messagebox object with a distinct parent, the scripts work fine, but I would rather not have to create new messagebox objects for each messagebox in the application.
I've heard of people having problems with the ~ActiveApp tag in their MessageBox objects, but I haven't run into it myself. May want to search the archives.
Additionally, you may want to see if there are any patches/hot fixes for SilkTest that address the issue. There are three HotFix's for SilkTest 5.5. I've heard that they are not cummulative; that is, HotFix 3 does not include the fixes in HotFix 2 or HotFix 1. Go figure.