Vue Scan not seeing serial

[thefrogs]

I have an existing copy of vuescan and a license but on uploading to  
the latest version the 'unlimited' upload doesn't seem to work  
because the serial doesn't seem to translate across. It still says,:  
" enter your serial here".
Can someone tell me where the serial is to translate it across by  
retyping. It is a long time since I bothered with the serial and I  
can't remember where I put it.
tom samson