Two cases that I've run into:

• create the same time-series collection twice: "A view already exists. NS: w16b10000mdb.a" should be come "A collection already exists" or "a time-series collection already exists".
• attempting to remove or update a measurement, yields: Namespace w16b10000mdb.a is a view, not a collection. It should instead mention that the operation is not supported on time-series collections.

This second case is handled in catalog_raii.cpp and will probably address a large number of different situations. Grepping "is a view, not a collection" also shows an occurrence in run_aggregate.cpp, so that should be changed as well.