Cannot build ROLAP dimension in SQL Server 2008R2

If I create a very simple dimension from 2 tables:

Table 1 (Master)               Table2 (Detail)

                                       DetailId (PK)

MasterID (PK)  <----------   MasterId

Caption                            Caption

Build a hierarchy on the attributes MasterId (Level 1) and DetailId (Level2)

and then set the storage mode to ROLAP the dimension will process but it is not possible to browse the detail level. The error message is "Server: The operation has been cancelled. The browser has encountered an error while querying the current hierarchy and has been disabled."

With storage mode set to MOLAP the dimension processes and displays without problem.

Am I being exceedingly dim today or is there an issue with 2008R2?