Certain sites have SharePoint Designer disabled.

Greetings,

There are certain sites in our SharePoint 2010 Enterprise environment which cannot be opened using SharePoint Designer.

Below is the message that I get.

I am a farm administrator hence permissions isn't the issue.

I have also looked into the onet.xml file in the SiteTemplate I am using and didn't find DisableWebDesignFeatures=wdfopensite.

Any help in this regard is highly appreciated.

Thanks in advance.