During my R&D work today, i come across a situation how to reset the password for rpd where I forgot the old password. All existed solutions (like NQSChangepassword.exe command) have associated with mentioning old password to get the new one.
The work around I found:
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Open NQSConfig.INI file
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Go to Security part and find AUTHENTICATION_TYPE = BYPASS_NQS;
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Uncomment (remove #) this part.
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Stop the BI Server service
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Close Administration Tool, if opened. (Then only the changes are affecting to the Administration Tool)
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Open Administration Tool, then rpd which needs password reset, in offline mode
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Give any password, it accepts.
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Now go to Manage > Security.
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From here it’s the normal process how you change password.
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Save the changes to rpd
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Revert back the changes in NQSConfig.INI
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Start BI Server and open rpd with new password.
I am not aware of whether it is this bug or something else. And there is also a way to do this using Import from Repository. But this is deprecated option. Of course, i found that my approach is an easy way and not time consuming process 
This is the work around I found for resetting password of rpd.