HTTP Error 500.21 – Internal Server Error
Handler "ChartImageHandler" has a bad module "ManagedPipelineHandler" in its module list
Moving an AbleCommerce Gold R4 install today created a weird error.   Site was moved from Windows 7 64-bit to staging server running Server 2008 R2.
Able Gold R4 ran fine.  Booted right up, logged in and no issues noted.  Until I clicked the Charts tab.  None of the graphs were rendering.   Just the little bad-image icon in my Google Chrome.
After a lot of digging, I found many posts saying to reinstall ASP.net.   I tried that, didn’t work.
So on a hunch I decided to switch my IIS application pool from ASP.Net 4.0 Classic to ASP.Net 4.0 Integrated.  BAM!  All the charts start rendering exactly right.
Apparently Gold R4 requires 4.0 Integrated.