Sometimes it happens that AROS crashes unvalidating the primary partition. This makes the HD0: disc read-only, and any change impossible. Unfortunately there isn't any validation utility yet, so the only way to make the HD0: partition working again is formatting and reinstalling AROS from a live-cd. Doing so, most of VmwAROS customizations will disappear, however you will be able to write on HD0: again.
To prevent this, VMware user can either create snapshots of their AROS virtual machine. It's quite easy: from the VM menu just select Snapshots and create one. It's quite like running Ghost or any disc-image backup software. A 280 MB big file will be saved within the VmwAROS directory of host operating system. You can revert to this image whenever you want. So I encourage to make a snapshot immediately after configuring the network and every other workbench option of your choice (wanderer background, theme, colors, keyboard layout, locale and so on). You will be able to have them back any time.
Be aware that reverting to a old snapshot will destroy everything you've done in the meanwhile, so you'll not find your recent working projects or installed applications anymore. Due to FFS fragility, I encourage you to backup often. If you don't need an older snapshot, you can always press Ctrl+M and delete obsolete ones with VMware snapshot manager to save space.