User and password not recognized

[Sanguinarius]

I'm having the same problem, only when I try and create a customer, it doesn't appear in the Admin > Customers section; however, I deleted a customer from the Admin > Customers area successfully.

1. Check that you're spelling the email address correctly. (yes, I know, that's obvious, but must be mentioned)

I am.

2. Does the customer account exist according to the admin area? (you said
yes)
Yes it existed for a long time and was used several time before

Same as above answer.

3. If it does, then check that you're using the same database-name and db-prefix name and database-server name in your configure.php files in admin and storefront.
I am using the same data base. I haven't changed anything really

Same here. I believe it is all correct.

4. Does the storefront let you create a new account using that email address?

No.

5. What addons/contributions do you have installed?

Braintree Payment module; 2checkout (?); USPS v15 Ratev3 2013_0127; tinymce-3.6.6; taxcloud_1.5.2_for_zc_151; zones - Lower48andDC; new-msrp-display_for_1.5; Keepalive Timer; Google+1_ Facebook_Send_V2.0; google_adsense; Google Translate for Zen-Cart; FCKeditor; Edit_Cart_v2_For_ZCv150; backup_zc_v1.1; zencart-2checkout

I believe I have all of the above installed.

6. Did the customer account get created by "you" or by a PayPal Express Checkout transaction?
This was an account I created at the begining of the original install last year

Likewise. Also, one customer account did NOT get created.

This explains why I've had NO sales and NO customers sign up since my install time. (a number of months).