After removing the license.licx file and if you don`t open or change any form there, all should compile fine.
This`s not a Flexible TreeView issues, this error appears because of VS SP1 installation. You can
google about that or see
here.
As a short answer, you need to install MS SDK but even after that there`s no guaranty that all will work fine. After installing SDK (if it doesn`t help) open Windows registry editor and create reg path HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SDKs\Windows\v6.0A\InstallationFolder with the value C:\Program Files\Microsoft SDKs\Windows\v6.0A\
Feel free to contact us if it doesn`t help.