Network connection problem

My family has three computers all running Win7 Home, 64-bit, forming a Homegroup: a desktop and 2 laptops. The desktop has an external hard drive which I have opened up via “Network File and Folder Sharing” as: “\Jc-server\m”.

All was well with Comodo Backup - my wife’s laptop connected and ran a backup successfully to this network drive.

After an auto upgrade to Comodo Backup, a window pops up requesting a username and password to connect to my desktop server. I’m baffled, firstly because it used to work fine without any id/password, and secondly because I set no such requirement up.

Can anyone explain what might be going on - and gently, please, I neither like nor understand much about Win7 security issues.

Thanks folks.