Windows 7: What causes prompt for Network password?

I've set all the Advanced Sharing settings as I always do, with no password for sharing, Network discovery, sharing allowed, but one PC on this network insists on prompting for a Network password when trying to connect to the other. It stopped for awhile but is back to doing it again now, also apparently blocking sync via Skydrive Skyshell. Is there another setting I need to check which I'm missing?

Hey Greg,

I'm sure you are aware of this but the time/date settings between those machines needs to be in sync or there will be problems.

Sometimes if the bios clock or the routers clock is off it can also cause problems.

I finally got it fixed on one by going over all the permissions, then it started up on the other one. Whack-a-mole.

Checking time/date now.

I wonder if it might also affect Skydrive which Sync is not working correctly for the first time in months.

They're both fresh installs of my folks' PC's, and I'm leaving tomorrow.