The string which comes from my data source is formatted like this:
2011-04-11 23:12:05
// dateString comes from my data
A date format string of @"MMMM" means that the string you're trying to parse is the full name of a month ("January", "October", etc).
@"MMMM"
You want something more like:
yyyy-MM-dd HH:mm:ss
Check out the date formatting patterns for more info.