cleartool: Error: Checkout disallowed for element "."

cleartool: Error: Checkout disallowed for element "."

I got the error while trying to check out the "." directory in clearcase.
FYI:
view is syncronized with the stream config and all components are modifiable.
The stream has foundation baselines as well as recommended baselines.
The vob is the component of ucm pvob.
cleartool co -nc "."
cleartool: Error: Checkout disallowed for element ".":
the component containing the element or the current stream is read-only
in this project, or the stream lacks foundation baselines.
cleartool: Error: Unable to check out ".".
How would you troubleshoot this error message?