The system cannot find the path specified. (Error code 3) at CMMFile::CMMFile: open file C:\Inetpub\vhosts\default\htdocs\index.html

Here is the error I got when, this happened with you are doing your initial server configuration for your plesk control panel.

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Error: Unable to update administrator information: The system cannot find the path specified. (Error code 3) at CMMFile::CMMFile: open file C:\Inetpub\vhosts\default\htdocs\index.html
==

The issue was that the path and file that it was looking for does not exists.

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C:\Inetpub\vhosts\default\htdocs\index.html
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Simply log into the server and create the folders and files then continue with the registration/set up.

Have fun!