Missing MSI’s/MSP’s error during SQL Server Patching
  Missing MSI’s/MSP’s error during SQL Server Patching Missing MSI’s/MSP’s errors will be coming    1. while Applying Service packs   2. While Installing SQL Server instance (another instance in same box)  Reason: As the error states a possible Windows Installer database file (.msi) or the Windows Installer patch file (.msp) is missing from the Windows Installer cache. This normally occurs when the setup is stopped mid-way or due to file corruptions.  Also As part of C drive space management windows team used to delete files from folder ‘ C:\windows\Installer\’   where our SQL Server instance dependent  MSI/MSP files are located. so if these files are deleted we will get MSI/MSP files missing errors while applying SQL Service packs (or) doing another Instance of SQL Server in the same server  Fix: Below is an amazing support link by Microsoft which explains the cause and resolution for the above error. It also provides a vb script...