error code for pop3 email -ERR invalid message number

I have just started using eM Client to replace Windows Live Mail which suddenly stopped working on 12/18/2017 after years of no problems. 

eM is setup as a POP3 account for email with the same settings I have been using (, 995, SSL) and will receive mail, but with a significant delay for when the mail appears in Webmail (the ATT online mail access).  Under Windows Live Mail, the POP3 mail was available immediately when the mail appeared in Webmail with no delay.  eM Client is set to check for new mail every 5 minutes, and usually generates an error message (-ERR invalid message number) but occasionally does receive mail and when this happens it receives all new mail since the last successful connection and then goes back to the error message.  The timing of successful connections varies - it may be 30 minutes or 3 hours.  

Windows Live Mail is on 3 computers and all three stopped working at the same time with the same error message.

I am using eM Client version 7.1.30794.0 on a Win 10 pc with Norton Security Suite.

These are the error and log screen shots:

Note the successful connections at 10:30 and 10:35 which are preceded and followed by errors.

Can you suggest any way to stop the error messages and receive the new mail immediately once it is available?

The errors aside, if you want to receive your email immediately, you need to setup your account as IMAP. This recent thread discussed how to do that.