Office Web Application access issue over SharePoint

Hi All,

I have installed OWA 2013 for SharePoint 2013 in a Farm and the same has been connected to the SP Farm. I'm able to access the OWA from all the SharePoint sites in the Farm, but the sites which are added to the Host header in the IIS causing this issue. 

Note: All the sites are Internal and for few of the sites are IIS Host Header Mapped sites.. 

Thanks in advance for your suggestions!

Arun

Arun Prakash