I was doing some work on a product today that uses .net extensions in SalesLogix. A problem was reported that one of the dependent assembly interfaces could not be located. I jumped on a gotomeeting to confirm that all of the assemblies were being registered from the correct location and had the right version numbers. Confusingly the assemblies looked correct but when registered one of the assemblies did not have the right version number. I decide to search the machine for other instances of the assembly and found that there were versions located in the program files\SalesLogix directory that had the suspicious version number. Once we deleted these rogue assemblies the extension manager resolved the child assemblies correctly. So if you have a problem with your assembly versions not matching up look in your saleslogix folder to see if an old version exists there.