Does it display any better in either of the external schedulers (OWB and MS Project)?
When a project does not display in the project list that is typically caused by -99 value in the last_update_by field.
If that were the case for the WBS in this case it would not display in the Clarity GUI either.
Another hickup I've seen recently was a non-ascii chracter in the task name, but that again threw an error in the GUI and did not display the task list either.