Certexams.com has recently updated CCNA NetSim (http://routersimulator.certexams.com/network-simulator-designer.html) to .NET compliant version. Please check it out.
A known bug, incompatibility with Adove 11 has been solved with the update. The product is still in beta version for field trials, and a stable release will come up in about 2 weeks.
Download page link:
http://routersimulator.certexams.com/ccna-simulator-download/download-network-simulator-designer.html
Please note that both VB6 and .NET versions available at present.