Warning :   Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.

Go to registry editor from Run--> regedit
Access the path  HKEY_CLASSES_ROOT\Installer\UpgradeCodes\3524D972551B58E4F98B4FCC185BFB8B

In the above Key, there will be more than 1 string value with GUID, which is causing this issue.

Delete the invalid string value with GUID representing the old version of Backup Exec to resolve the issue. Only the string value with GUID of the currently installed Backup Exec should be present there.

After deleting the value, run the repair or license install wizard to verify it works as expected.

GUID for some of the Backup Exec (BE) versions are given below.

BE 24      - 3118DC4CB889EB84CACD059B31579FB1 
BE 21     - 957BFB912435E0B4999A71B1C660009F  
BE 20     - C217ADD0DA67F7C4DA58A55C72943438
BE 16     - 9AB7C3BF21D7D6B429065F84D807654B
BE 15     - 43F936BCCD75314479264C54D0E52126
BE 2014   - F7F1709B5241DDE41BCA298A93EABA04
BE 2012   - 573FC710CCCD71743B2A5F94EC45DB5E
BE 2010    - 849601AB3B45F3A4B9218906A2BADF34


You can find which is the GUID for the currently installed Backup Exec, from the register entry below as well. You must remove the string value of BE which is not present on the BE server.

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Installer\UpgradeCodes\3524D972551B58E4F98B4FCC185BFB8B