Aria Operations 8.18.x
The issue is caused by the presence on vCenter of several VMs with unconventional names starting with the symbols "$" or "%".
Those VMs are usually created created on vCenter by the penetration test.
There are two options:
OPTION 1
Renaming the VMs to a conventional name.
OPTION 2
Deleting all the VMs with names starting with "$" or "%" if the VMs were created on vCenter by the penetration test.