What's the version / localization of your SQL Server?
I tried it with SQL Server 10.0.5500, German localized Management studio. I adjusted the date format of your query, and tested it. And it worked as it was expected to work - I cannot reproduce your bug.
Msg 1823, Level 16, State 2, Line 1
A database snapshot cannot be created because it failed to start.
Msg 7928, Level 16, State 1, Line 1
The database snapshot for online checks could not be created.
Either the reason is given in a previous error or one of the underlying volumes
does not support sparse files or alternate streams. Attempting to get exclusive
access to run checks offline.