Hello,
I just switched from Ubuntu to Kubuntu due to the fiasco that is Unity and have everything working except for a problem with Krunner. I'm running Kubuntu natty 64 bit and had the problem right after a fresh install. I also just finished adding the ppa to get 4.6.3 and just tested again and still have the below issue.

If I use Alt+F2 and then smb://server/share to connect to administrative shares on windows boxes (c$), the system prompts me for username and password at least 5-10 times before finally showing me the share. I use domain\username and password format.

I know I get the credentials right because they are cached and it finally shows the share to me rather than denying access. I can't really map these drives in fstab because I am an admin providing support to windows users on demand and have to map their drives as needed.

If you use the same credentials across all the computers, try setting your credentials in System Settings > Sharing > Windows Shares.