Managed reporting would mean that the reports are stored in the CMS database and need to be retrieved using the CUID. Version 13 assemblies do not support Managed reporting. Only version 14 assemblies do.
Unanaged RAS (e.g.; reports are loaded from some HD path) should be fine using RAS or CR SDK.
As for the error. Understanding the history here (I think 
), I'd like you to have a look at this Discussion:
errors when calling Crystal report from dotnet
In a nutshell the solution was to make sure v14 and v13 assemblies are not on the same computer.
There are a few other possibilities, e.g.;
1329713 - Error "Document has not been opened" while initializing ReportDocument object
but I think the v14 v13 incompatibility is it (fingers crossed).
- Ludek