In the past, when adding one off assignments, issues have been encountered where the “Select Carer” drop down would not unlock.
This is because some data was not being added in properly and ultimately skipped. Starting from “Assignment Type” work your way down the list, filling out each box as you go - date commenced, start time, end time and location.
Should this happen to you, press ctrl & F5 together to refresh the page, (CMD R for MAC) and restart the page filling in all boxes as you go. This will solve this issue.