MS project - cannot change working day

[msprojectuser50]

When I select a task in order to move it from a normal work day to a Saturday or Sunday selection it pulls up the selection box with two options. The first option is to move the task data to the next working date which I do not want.
The second option is make Sunday a working day that I need, but this option is shaded out.(See attachment)

This appears to be some type permission issue that our adminstrator cannot determine at this time. Has anyone run across this that could assist me?

Thanks

[EINSTEIN_007]

Try to do the following and check if that solves your issue:

• Format
• Timescale
• Non Working time pad
• Select the new calendar to show.

Another way of doing this is might be choose Tools -> Chaneg Working Time…
Choose the standard calender and dont include an exception for Sundays.