Unable to update macOS Catalina 10.15.4

Try using the macOS Catalina 10.15.5 Combo Update.  If you still have problems with out boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and apply the updater from there.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing. 

Hey there kailashchhetri,

Thanks for reaching out to Apple Support Communities. It sounds like you’re running into issues when attempting to update macOS. We understand the importance of being able to keep your Mac up to date and we’ll be happy to help with this.

How are you attempting to update? Review the following link to make sure you’re going through the expected steps:

How to update the software on your Mac 

If that’s not working, try manually downloading and installing the updating from here:

Download macOS Catalina 10.15.5 Update

In that case, you’ll need to manually start the update once the download is complete.

If you still run into issues, boot into safe mode or a new user account and try updating there:

How to use safe mode on your Mac

How to test an issue in another user account on your Mac 

I hope this helps. 

Take care.

I also have this problem of trying to update to macOS Catalina 10.15.5 on my MacBook Pro and have tried to download with Safe mode and also the Combo update. Neither work - the messages say "The installation failed. An error occurred downloading one or more packages for the update product". Would be grateful for some assistance.

How much free space do you have on your boot drive?

938 GB

Well that shoots another brilliant theory down.

You might try this: log into another admin user account (or create one to use) and try the installation or Combo updater from there.

Thanks,

Will try that.