What causes XP to stop sharing files and folders over a network. On occasions folders are automatically prevented from not sharing and the option to enable sharing over the network becomes greyed out. This is strange since no IP or Network configuration changes are made. I get a feeling this can occur when say for example the hosting PC (and hub)are turned off before the client thus creating a broken link. Is it good practice to have the hub permanantly switch on?

There should be no problem in leaving your hub on, although switching it off/on should not prevent you from sharing thru the network. I has a similar problem with XP not being able to share a drive, a reinstall of XP solved the problem with no data loss.

Also - if there is a change in The Force (one of the computers in the LAN is taken off line) you may have to wait a few minutes for all the computers to update.