text field in form not allowing input

[Bob H]

I have a database with several text boxes/fields where I input daily data.
Just recently, one of the fields does not allow input of data, and I
have to input the data into the associated table, which I know I
shouldn't have to do. Then once the data is in the table, the text field
on the form does allow input.... weird!

This has happened about 2/3 times over the last few weeks, and I haven't
a clue as to why it has.
I have checked the field properties but nothing looks out of the
ordinary for the said feild.

Any ideas please as to why this happens just now and again.

Thanks