Find the answer to your question
When version of the .NET SDK should I be using?
What is the oldest version that I can safely use?
We recommend that you use the most current version of the SDK available if you are developing towards a software release.
The minimum recommended version is v447
Technically you can use older versions such as 3.1.0 which was based on the 419 WSDL (this version is no longer available for download)
Please be aware that using the 3.1.0 version uses some features that we recommend should not be used, such as ModifiedFields on ReviseItem.
Other concerns are the change from SiteHostedPicture/VendorHostedPicture to PictureDetails which occured on the 439 WSDL release.