Ok, I fixed it up for you.
There seems to be a problem in Access when you try to remove the focus from a subform to the mainform, there is also a focus maintained on the subform. What I did was make an unbound textbox on the subform named "txtFocus" and set it's width to ".1" so you can't really see it. This will take the focus on the subform when things get disabled.
The second thing I fixed for you was the Date() function, I've seen this done before, at some point in time you named a control or field "Date". Once you do this, the Date() function is erased, meaning you can't use it again (unless you can find out where in Access you can fix it).
Anyhow, here is the updated database with my fixes, hopefully this helps and finally works for you!