Hi there and many thanks for your post!
The attribute you mention ("AddAssemblyToExceptionReportsAttribute") was something of an undocumented "hack" back in version 5 to get error details from secondary assemblies, but there are now two different options to get this functionality with SmartAssembly version 6. In order to do this though, SmartAssembly would need to instrument each of your secondary assemblies, which I'm very sorry to say means the two options may not be optimal in this case..
To get error information across multiple assemblies, you'll either need to
1. Merge the assemblies into your main assembly
2. Process each individual assembly with its own SA Project and enable error reporting on each one (as described here: http://www.red-gate.com/supportcenter/C ... rrors_DLLs
I realize that merging is not an option since your assemblies are loaded at runtime, so I'm afraid that enabling error reporting on the individual assemblies would be the only other way around this in version 6. :/