SSRS: rsErrorInOnInit error

I came across the following error when trying to print a report in Dynamics AX 2012:

Error while setting server report parameters. Error message: An error occurred while executing OnInit: The report execution failed to start. Verify that Report Extensions have been installed or are configured correctly.
Please consult your administrator or the documentation. (rsErrorInOnInit)

An error occurred while executing OnInit: The report execution failed to start. Verify that Report Extensions have been installed or are configured correctly.
Please consult your administrator or the documentation. (rsErrorInOnInit)

I was installing multiple SSRS instances on one server, other instances were working but this particular instance was not.

If you have multiple SSRS instances installed on one server, you have to make sure that the configuration files for all instances are modified correctly.
To solve the above errors, I performed the steps as describe here for the instance that wasn’t working: Modify Reporting Services configuration files [AX 2012]
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