Thank you for the response. However, I had already run through the troubleshooting process.
I have now resolved the issue, and in case it is of benefit to other users who encounter the problem, I will describe the bizarre steps that worked:
- When I input the credit card as a continuous string of 16 digits, the "Save" button remained inactive, but there was no warning that there was a problem with how I was inputting the card number.
- I then inserted dashes to separate the 16-digit credit card number into four 4-digit groups (XXXX-XXXX-XXXX-XXXX). This caused the "Save" button to become active, but when I left-clicked it, an error message stated that the card was not of the correct "type".
- I then removed the dashes from the number (thus reinstating the way in which I had first input the number). The "Save" button remained active, but this time, when I left-clicked it, the card number was accepted.
I suspect that many people will think that this cannot have happened - that I made a mistake keying in my credit card number - but this is definitely not the case. I had tried many times to input the details, using 3 different browsers (Firefox, Internet Explorer and Opera) with 2 different operating systems (Windows XP and Windows 7). The result was the same every time.
It remains to be seen whether Adobe will recognise, and do something about, this Kafkaesque programming bug.