Web application error after upgrade to v8

Question

Hello Experts, 
 We have upgraded our 7.1.2 installation to v8, and the database was upgraded successfully. We als 
 We installed a new web application (source selected was the installation media not the DB) but when browsing to the link, we get a 500 - Internal Server Error 
 I checked the logs, and there are some messages of the kind: 
 Script Assembly Webapp_VI_StandardWeb_Debug_AP not found in 'DialogScriptAssembly' 
 The v7 web portal had a lot of customisations. 
 We are a bit stuck here, any idea why that error is showing up, and more importanty, how do we fix it? Do we need to uninstall the existing v7 portal instead of installing a new one? 
 Thanks 
 Kin

Paul Walker · Accepted Answer

Use webdesigner to attach to your old web portal and compile/fix any compilation errors in order to migrate your customisations. I would use the install media to uninstall the new clean OOTB web portal so you just have the old one present. 
 
Foe info, there's a dB table that details the web applications that are installed in your OneIM system, can't remember the exact name tho sorry 
,It had web and apps the name. But best practices is to use the installation media to add/remove the web sites.