...\EventHandling.fs(99,20): error FS0407: The mutable variable 'cts' is used in an invalid way. Mutable variables cannot be captured by closures. Consider eliminating this use of mutation or using a heap-allocated mutable reference cell via 'ref' and '!'.
Look at https://ci.appveyor.com/project/dungpa/visualfsharppowertools/build/2.6.0-a1607121916
and an error conforming F# 3 is used: