Upgrade error: Can't add group psaadm

[JBxOnline]

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PRODUCT, VERSION, MICROUPDATE, OPERATING SYSTEM, ARCHITECTURE
Plesk Panel 10.0.1
Centos 5.9
x86_64

PROBLEM DESCRIPTION
Upgrade is unable to add group psaadm (already exists)

ANY ADDITIONAL INFORMATION
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Here is the output of my error log:

===> Checking for previous installation ... found.
Create user 'psaadm' and group 'psaadm'
Checking for the group 'psaadm'...
Trying to add group 'psaadm'... groupadd: group psaadm exists

ERROR while trying to add group 'psaadm'

I'm attempting an upgrade to 11.0.9 via the GUI.
Any ideas?

Thanks guys,

Jon