Event ID 1020 Source: TermServSessDir

The "Session Directory Computers" group is empty, you must add the computer accounts of Terminal Servers into this group for the Session Directory Service to work properly.
Source
To Do This: Do it on the Session Directory Machine:
1. Start - Execute
gpedit.msc
2. Browse to Local Computer Policy\Computer Configuration\Windows
Settings\Security Settings\Local Policies\User Rights Assignment
3. Open up "Access this computer from the network"
4. Add in the Terminal Servers that will be connecting to this Session
Directory Server
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Source
Populate the Session Directory Computers group

To resolve this issue, add the computer accounts for the terminal servers that will be members of the load-balanced terminal server farm to the Session Directory Computers local group on the TS Session Broker server.

To perform this procedure, you must have membership in the local Administrators group, or you must have been delegated the appropriate authority.

To add computer accounts for terminal servers to the Session Directory Computers local group:

1. On the TS Session Broker server, open the Local Users and Groups snap-in. To open Local Users and Groups, click Start, click Run, type lusrmgr.msc, and then click OK.
2. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Continue.
3. In the left pane, click Groups.
4. In the right pane, right-click the Session Directory Computers group, and then click Properties.
5. Click Add.
6. In the Select Users, Computers, or Groups dialog box, click Object Types.
7. Select the Computers check box, and then click OK.
8. Locate and then add the computer account for each terminal server that will use the TS Session Broker server.
9. Click OK to close the Select Users, Computers, or Groups dialog box, and then click OK to close the Session Directory Computers Properties dialog box.

Verify

To verify that the Session Directory Computers local group on the TS Session Broker server is configured correctly, ensure both of the following:

• The Session Directory Computers local group exists on the TS Session Broker server.
• The computer accounts of the terminal servers that use the TS Session Broker server are members of the group.

To perform this procedure, you must have membership in the local Administrators group, or you must have been delegated the appropriate authority.

To check the configuration of the Session Directory Computers local group:

1. On the TS Session Broker server, open the Local Users and Groups snap-in. To open Local Users and Groups, click Start, click Run, type lusrmgr.msc, and then click OK.
2. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Continue.
3. In the left pane, click Groups. Ensure that the Session Directory Computers group is listed.
4. In the right pane, right-click the Session Directory Computers group, and then click Properties.
5. Under Members, ensure that the computer accounts for all the terminal servers that use the TS Session Broker server are listed.

Related Management Information
TS Session Broker Security Group Configuration
Terminal Services
http://support.microsoft.com/kb/823659