There is 1 error Authentication failed Prestashop 1.6

[asoulja]

I am using Prestashop 1.6.1.5 and recently migrated my store to  1.7.5.0. The 1.7 store is in development currently so I am still running the 1.6 store as my live site. Customers have been complaining about having login issues. When they try to login with their information and password they are getting 

There is 1 error

1. Authentication failed.

I have tried myself and get the same error. Customers and myself included have to change the password and then it works. Then when the session is over and they try to login again the same error comes up. If anyone knows about this error or if there is a fix for this please share. This is occurring on the 1.6 store and not the new store in development (havent check that as of yet). Any help would be much appreciated. Thank you