What are the Sched Capacity settings on WC3?  The shop order is due today, so are the resources for the WC3 already consumed today?  That is most likely the case.

@ShawnBerk ,

The shed capacity is infinite.

When the shop order is backwards scheduled it ends up on a date earlier than when any capacity is available for the work center resource. If you look at the Resource tab on the work center and check the date availability there it should be more clear. If you then create a new line for a date range before the existing earliest range the shop order should be possible to save (and schedule). Else you can change to forwards scheduling and it should also be possible to save.

Dear @ShawnBerk  and @Björn Hultgren, with the help of the above guidance, I changed the need date and finish date accordingly. Now, I was able to save the shop order.  Thank you both of you.