For some reason that registry settings sometimes gets messed up, I'm not sure what causes this to happen.
First make sure that Homegroup permissions are set to "Everyone" read-write on all machines. Also make sure that live essentials real time protection it enabled on all machines.
Note, If the DisabledComponents entry is unavailable, you must create it. To do this, follow these steps:
Just a Note here Create a DWORD -> DisabledComponents
Navigate back to where that registry key is supposed to be.
1. In the Edit menu, point to New, and then click DWORD (32-bit) Value.
2. Type DisabledComponents, and then press ENTER.
3. Double-click DisabledComponents.
# Type any one of the following values to configure the IPv6 protocol, and then click OK:
4. Type 0 to enable all IPv6 components. "
If that doesn't fix the problem try delating the following file to fix the problem.
Delete the file idstore.sst under C:\windows\serviceProfiles\LocalService\AppData\Roaming\PeerNetworking