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Hello all. I am new to zen cart and have searched for a remedy to my issue but have been unable to find anything. I apologize if this ia a duplicate post.

https://www.made-right-here.com

ZC version: 1.5.5 installed by FTP
THe only plugins I am running are taxcloud, shipstation, UPS tracking, and the Winchester BLack template
PHP version 5.6.37
MySQL version: 5.6.41-84.1(as it is listed in the server info under admin>tools.)
I do not know for certain when the problem started, Only that I noticed it last night when I was doing some shopping cart test runs to make sure everything was running smoothly.

Problem:
anytime there is a login, logout, or change in the shopping cart contents I get the following message:

Made-right-here.com says:
An unknown response 400: :text/html; charset=utf-8: : was received while processing an ajax call. The action you requested could not be completed.

In my browser, the message shows as a pop up with an "OK" button. WHen I click the button, the action continues and is apparently completed. THis happens when loggin in as a shopper, or when browsing without being logged in if I add something to the cart login. I have had no such messages in the admin area. I have not tested actual transactions yet to see if this affects them. THere do not appear to be any related debug logs. I will include a screenshot of the message. Please let me know if there are other questions or needed information.
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