Troubleshoot a 'Sys' is undefined message in my upgraded web application

Question

I have a web application that was originally written on .Net 1.1 Framework. I have since tried you upgrade it to .Net 3.5 Framework. I am now getting this javascript error throw on my page and for the life of me can't figure out exactly why.

I have target the application for the .Net 3.5 framework, and even deleted and added back in the web.config file. Any ideas on what to do to troubleshoot this?

Update 1/20/09 6:44pm

I verified my httpHandlers, per @Zhaph Ben Duguid section looks good ... Created a new WebForm1.aspx page added a script manager and still getting the same error.

Resolution

It was an old component art javascript library that was throwing the error.

Answer 1

I'd guess there's a missing javascript library - check your access logs to see what requests are generating a 404.

Answer 2

I tend to use FireBug in Firefox - it allows you to see the contents of each dynamic .js file - you'll probably find that one of them is producing either a 404 or a 500 Internal Server Error.

Without knowing which AJAX framework you're using, I can't really help all that much, but I'd take a look at the httpHandlers declared in the web.config, you should probably see some entries like:

 <httpHandlers>
  <remove verb="*" path="*.asmx" />
  <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
  <add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
  <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false" />
  <add verb="*" path="*.mvc" validate="false" type="System.Web.Mvc.MvcHttpHandler, System.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
 </httpHandlers>

These are for the standard .NET 3.5 script libraries, yours may well be different.

But take a look in there, and ensure that the libraries referenced are available - compare this section with the same section from the original 1.1 web.config - that should get you on the right track.