To use the source code you need to get it using Tortoise HG, but you also need to understand that the latest source code is newer than the release packages and has many changes since the 2.3.6.7 release.
If you want source code that corresponds to the 2.3.6.7 release you should get the code with Tortoise HG and update to revision 2381 using HG > Update command
If you want to work with the newer code then after you rebuild the solution you must visit the /Setup/Default.aspx page so it can run upgrade scripts which would create any new stored procedures.
The download links for source code on codeplex are generated by the codeplex web site and often seem to be incomplete or incorrect, the only correct way to get the source code is using Tortoise HG.
Hope that helps,
Joe