It is important to validate your current CRM system before upgrading to CRM 2013. Be sure, to run the CRM 2013 Custom Code Validation tool (available on codeplex)
It will detect issues in the custom web resources that will no longer work after the upgrade is completed. The most common issues that this tool targets are –
- CRM v4 client SDK calls
- CRM 2007 end points
- Common DOM manipulations
Running this tool before upgrade will enable you to identify issues and fix them prior to your scheduled upgrade so that your upgrade process can run smoothly.