MMA 2012 R2 Update/Uninstall Error: This Patch Package Could Not Be Opened

Issue
When trying to update/uninstall a SCOM 2012 R2 Microsoft Monitoring Agent (MMA) this error can be thrown: This patch package could not be opened. Verify that patch package exists and that can access it.

Cause
Registry corruption.

Fix
Simple and straight forward. Follow this procedure:

1. Start regedit. For SCOM 2012 R2 MMA locate this key: HKEY_CLASSES_ROOT\Installer\Products\5C0796876F6E14A42B83EA524D9BE1AE\Patches.
2. Make an export of this key before proceeding!!!
3. Find the REG_MULTI-SZ entry Patches, open it and REMOVE all entries > OK.
4. The update (UR installation) or removal of the MMA runs just fine now.

Tips & Tricks
When running SCOM 2012 RTM MMA, the regkey should be: 9D603783EC87E0E49B25825AC0.

When running SCOM 2012 SP1 MMA, I don’t know the regkey, but the registry edito will help you:

1. Start regedit. For SCOM 2012 R2 MMA locate this key: HKEY_CLASSES_ROOT\Installer\Products
2. Hit <CTRL> <F> and type Monitoring Agent in the search box > Find Next;
3. Soon the correct key will be found. To be sure, check the ProductName entry. It should have this entry: Microsoft Monitoring Agent. When it does: Follow Steps 2 to 4 of the Fix.