?
Generally, load errors are logged to the BuildMaster error log within the software. You could also get live log messages by following this article. Periods in the assembly/file name are allowed, so that must have been unrelated. It's also worth double-checking the extension overview page which will show the load errors, but they don't immediately jump out:
For additional troubleshooting with regard to extension loading:
make sure to restart both the BuildMaster Windows service and web application service or IIS application pool once the file is added to the Extensions path
make sure there is a BuildMasterAssemblyAttribute specified in the project (normally in AssemblyInfo.cs)
the project is targeting the v4.0 or v4.5 version of the .NET framework
the file name, the assembly name, and the containing .bmx file all match (i.e. "CustomExtension.dll" should have the assembly name "CustomExtension" and must be contained in the zip file "CustomExtension.bmx")