Hi, After upgrading to Appian 7.6 our custom code throwing exception below:

It looks like it can not find a specific class, did you migrate over all custom libraries during the upgrade?

Hi Tim, Looks like Post platform upgrade issue - Brief description is as below:

•          Class com.sun.org.apache.xerces.internal.parsers.DOMParser was not available in classpath on but was available in compile bundle so deployment never failed. Class DOMParser was being imported from com.sun package rather than apache package in ComplianceUtils.java.
•          New product configurations already included extended xml-apis classes in calsspath. This could be possible root cause of the issue as DOMParser class was being referred by two different class loaders causing trouble in reading proper definition of the class.
•          Updated ComplianceUtils.java file imports to read class from “org.apache.xerces.parsers.DOMParser” package rather than “com.sun.org.apache.xerces.internal.parsers.DOMParser”

Not sure if some packages are removed or\\and added in new version. Atleast i can see xml-api3 is in.
Thanks, Ritesh