Cannot uninstall sheetnode

After unchecking all dependencies, and removing all content types and instances of content types with sheetnode data, I still could not uninstall the sheetnode module, because "Fields pending deletion" kept the checked box in the 'Enabled' column grey.

The remedy was to remove the sheetnode directory from sites/all/modules, refresh the module list, then return the directory. Then I could uncheck the Enabled box and Uninstall the module.