Very strange plesk backup error

[yatint]

Hello

for all my domains I am getting below error while taking backup using backup manager :

<?xml version="1.0" encoding="utf-8"?>
<execution-result status="error">
<object name="server" type="server">
<message severity="error" code="KeyNotFoundException">
<description>The given key was not present in the dictionary.</description>
</message>
</object>
</execution-result>

Any suggestion >