I’m not sure what caused my setup to produce this error, but after searching for a while and not finding any reason, I just added the lib directory and all was good. I was getting this when doing command line compiles and when using the spark view engine. I hope this might save me or someone else some time in the future.

error CS1668: Warning as Error: Invalid search path ‘C:\Program Files\Microsoft SDKs\Windows\v6.0A\lib’ specified in ‘LIB environment variable’