Hi @Puneeth, C ,
1.Try to delete site group with Power Shell. Code show as below:
Add-PSSnapin Microsoft.Sharepoint.Powershell
$spWeb = Get-SPWeb "https://sp/sites/yoursite"
$GroupName="testgroup"
if($spWeb.SiteGroups[$GroupName] -ne $null)
{
$spWeb.SiteGroups.Remove($GroupName)
$spWeb.Update()
Write-Host "Group Deleted!"
}
else
{
Write-Host "Group doesn’t Exists!"
}
2.If Power Shell doesn't work and you still get the "Group cannot be found" error, you'd better check to see if the ID of the group URL has been changed for some reason. Modify the ID and test if it can be deleted.
Reference to third-party article: SharePoint 2010 “Group cannot be found” error
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