Sorry Kenneth, I thought I had replied to your comment yesterday. I obviously didn't hit the submit button??
My response was, no, I didn't use CDate and that I haven't actually heard of that term before. So I'll have to look it up sometime, always good to learn something new.

Thank you everyone for your help.
I ended up going for 

DateSerial(Year(TextBox1.Value), Month(TextBox1.Value), 1)
Thanks David000

As this was the easiest to implement within my current code.
Problem solved.
Thanks again.