I have a user that runs a report in RTC and one of the options is to print to Excel. When you preview the report it tries to create an excel worksheet but gets the following error message: "This message is for C/AL Programmers. The call to member Range failed: Exception from HRESULT:0x800A03EC. The report runs fine in classic. The build is R2 32384.
If it is just the one user, then I would look closely at which version of .NET framework they have running on their workstation.
If that doesnt help, have a look at
http://msdn.microsoft.com/en-us/library/6s0wczt9(v=vs.80).aspx