I am having this same problem with SmarterMail 6.6. I need to import, into a mailing list, a CSV file with over 2,000 email addresses. SmarterMail refuses to let me import the list. I've carefully combed through all of the addresses to find illegal characters, quotes, anything to which SmarterMail 6.6 might object. Apparently I am missing something.
I have also tried to create and import a small CSV file, with just a few addresses, but I have had no luck with that either. I get the same error message: "Unable to import subscribers. The file is invalid."
Has anybody heard of a workaround for this problem? I need to set up this large mailing list soon. Thanks for any advice.
Eric Bourland