I've moved the build process to a new computer which has broken the configuration, it seems. I think that's why some of you are seeing errors on startup. Hopefully I've fixed that now, so to test, here's a new Construct.exe file:
http://www.scirra.com/files/construct09942exe.zip
Save it over your existing Construct.exe file and let me know if it launches properly now. If it does, I can try get a new build in ASAP!