Webservices fail with "SAXException occured while parsing the SOAP Document" after PT upgrade 8.52

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Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit
PeopleTools 8.52
HCM 9.1
FMS 9.1

Issue:
Created a new webservice and published from PeopleSoft on 8.51. Tested successfully using SOAPUI and worked fine.
Then tools were upgraded to 8.52 and the same service started failing with the above mentioned exception.

Try this solution:

1. Go to the Gateway Administration Page and then to the Advanced Options.
2. Change the ig.dtdLookup value from 'false' to 'true'. Save the changes.
3. Bounce the Web Server.