I had an issue with updating when an alternative calendar plugin was active. Specifically when All-In-one-calendar was active. To safely update Sign-up sheets you'd be advised to first disable any calendar related plugins.
I tested this on local site and it worked (not disabling the other calendar plug in generated the following errors:
Waring: array-Search() expects parameter 2 to be array, object given in /mywordpress site server path to alternative plugin php file/ on line 160
Fatal error: Cannot use object of type stdClass as array in /mywordpress site server path to alternative plugin php file/ on line 160
Updating to 2.0.12 after disabling that alternative calendar plugin, and the activating the alternative calendar plugin works, for me at least.