Cannot install new products or updates using the Symantec Installation Manager after it updated to the newest version. "Log in using application identity user credentials and try again"

Cannot install new products or updates using the Symantec Installation Manager after it updated to the newest version. "Log in using application identity user credentials and try again"
 

Cannot continue to run install product/update product/repair product/install hotfix with the current logged in credentials. Log in using application identity user credentials and try again.
 

A change was made to the Symantec Installation Manager to make sure all installs and repairs are done using the Altiris Service ID, known as the AppID or SMP Application Identity.

This is part of the fixes and changes done in ITMS 7.6 HF4. Please refer to Release Notes (DOC8949):
Under Page 8:
Note: To upgrade to the lastest hotfix, log on to Notification Server with the SMP application identity credentials.
As well it is mentioned under the Fixed issues for Symantec Installation Manager (Table 1-9)

1. From the Windows 'Run' box type 'services.msc' and hit enter
2. Find the 'Altiris Service' and look at the account under 'Log on As'
3. Make sure to log into the server as the account that you found in the last step and open the Symantec Installation Manager