Hello!
Thank you for studying them, and for confirming that the problem lies in the file named 5f6db.msi itself and not QuickDiag.
As it happens, I also have another file named 9acb635.msi, which is equal in date/time, size and MD5, which also is corrupt.
[2015.05.08 07.17.50 | 010,526,720 | ---- | M] () MD5=B3315DBDB28BD24D3AA4AC70566DCECB -- C:\Windows\Installer\5f6db.msi
[2015.05.08 ...