• You attempt to update your FTP password for a domain in the Plesk Control Panel
• The hosting plan for that account is a PERSONAL hosting plan or an ESSENTIALS hosting plan
• You receive the following error: Error: Unable to update hosting preferences: Unable to use shared IIS Application Pool: this feature is currently unavailable due to IIS Appliacation Poll mode policy.

Answer:

In short, the error you are receiving is a side-effect of the particular restrictions we put on the PERSONAL and ESSENTIALS plan and the way Plesk organizes permissions.  We are working on a method to modify these permissions to allow you to reset your FTP password without this error.  Please submit a support request, specifying what you were doing and the error you received, or reference this KB article.

If you can change an FTP password on another plesk account, it's because the hosting plan you have for that one is not a PERSONAL hosting plan or ESSENTIALS hosting plan.