We are having a trouble with calendar within our SharePoint site. The issue is that user would like to import events into calendar using the JS grid for the calendar list. However, he can't set the value of the column "All Day Event" as it's grayed out.
The workarond that we thought would work, was to create additional yes/no column, and when item would be created/updated, run a workflow that based on the value of the new column value would set proper value on the "All Day Event" column.
We have tried with setting the field value to 1/0, true/false but it always failed saying that the field require different information type. Have you been able to set value of the "All Day Event" column via workflow?