Check the XSD value in  web.config 

Example of a previous fix-

old value:

 <add key="XSDValidaterUrl" value="https://pa3.practiceadmin.com/PAEligibility/EligibilityXMLFormat.xsd"/>

new value:

 <add key="XSDValidaterUrl" value="https://pa.practiceadmin.com/PAEligibility/EligibilityXMLFormat.xsd"/