This occurs because Google detects that you're signing in from a location outside of your normal routine (e.g. ReplyManager server) which triggers a red flag. To get ReplyManager reading correctly, you'll need to verify that ReplyManager was given the necessary permission to access the account. To do this, you should configure 2-Step Verification in Gmail.
What is 2-Step Verification?
2-Step Verification is a security feature in Gmail that helps protect your account, even if your password is stolen. This provides extra protection because signing in requires two things: something you know (your password), and something you have (your phone).
How to Fix It
There are a few steps to implementing 2-Step Verification for Gmail and ReplyManager. You must follow through all in order to get things working properly again.
STEP 1: Enable 2-Step Verification
In Gmail (or any other Google account window), hover over your profile icon and click on My Account.
Review the information and click Start Setup
Enter the verification code and press Verify.
Press Confirm to turn on 2-step verification.
STEP 2: Generate a Special Password
So now that you've activated 2-Step verification, you'll need to generate an application-specific password for use inside ReplyManager.
Go to the App-Specific Passwords tab and click on Manage Application-Specific Passwords to generate a special password used ONLY by ReplyManager.
Using the Select App drop-down, select Other (custom name).
Enter ReplyManager in the field and click on Generate.
Copy the password to your clipboard.
STEP 3: Configure ReplyManager
In ReplyManager, go to Maintenance > Accounts, select account. Enter your Gmail username and the password that Google created. Save Changes.
Please note that when you enable Google's 2-Step Verification, you'll need to go through Step 2 above for each device you access mail with. We recommend only using ReplyManager to check the configured account. For more information about Google's 2-Step Verification, go to http://www.google.com/landing/2step/
Go to the App-Specific Passwords tab and click on Manage Application-Specific Passwords to generate a special password used ONLY by ReplyManager.
Using the Select App drop-down, select Other (custom name).
Enter ReplyManager in the field and click on Generate.
Copy the password to your clipboard.
STEP 3: Configure ReplyManager
In ReplyManager, go to Maintenance > Accounts, select account. Enter your Gmail username and the password that Google created. Save Changes.
Please note that when you enable Google's 2-Step Verification, you'll need to go through Step 2 above for each device you access mail with. We recommend only using ReplyManager to check the configured account. For more information about Google's 2-Step Verification, go to http://www.google.com/landing/2step/