I hit this recently, debugged it and fixed it.  If I recall, the answer is in the temporary install folder that the installer creates.  First off though, please ensure you run the installer as admin - I think that fixed it for me (though I was working through a bunch of stuff at the time so may be getting this one confused with another issue).

Obviously there is in fact an 'orphaned' installation.

On Windows you always have the opportunity/last chance to use the registry:

  - search for "EMC" and "Legato" and remove all NetWorker specific entries

  - Then remove the NW diretories

  - Reboot the server

Now you should have a clean system to try another installation attempt.

This is kind of conman issue when the older or newer version not removed or installed properly.

on support site you can find number of KB article for same kind of issues that tells you to remove the binary and registry entry.

Its seems some of the windows component is still holding netwokrer client hence you need a full removal of networker client first.

There is lot of 3rd part tool for removing complete windows package you can have a try with those and do the clean up.

or else You can follow these steps I found previously in some other post which worked for me also -

Remove the Upgrade Code from the following registry keys:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\Upgrade Codes

HKCR\Installer\UpgradeCodes

Windows Installer uses a GUID (Global Unique Identifier) to uniquely identify products being installed. They call it an Upgrade Code. This is used to identify that NetWorker is installed on this machine.

NetWorker has three upgrade codes (the first for NW 6.0, the second for all other NW versions (except X64), the third for the X64 package):

3EB2C626C9BC4D118811000972CCA7DF

2827A1B508153D114831000A9C877BD1

1D09C7743451200439D99949BD5A9F1E

It may also be necessary to remove the NetWorker services from the registry. They are located in:

-HKLM\SYSTEM\CurrentControlSet\Services

-Delete the following keys: nsrd, nsrexecd, nsrpm, hagentd, lgtolmd

-For NMC, the key to look for is: gstd

-After removing the services, reboot the machine.

Also run the below commands on the command prompt before you reboot the machine

sc delete nsrexecd

sc delete nsrd

All installed products have an entry in the following registry key:

-HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall

-Control Panel Add/Remove programs gets its information from this key.

-If an entry under this key is deleted, it will not be displayed in Add/Remove Programs.