I am using wpcf7 and wpcf7 simple captcha and they are working just fine. If you want to know, here is the site (new, experimental): http://www.bcstar.nl/0/
However:
In the process I created a trial WP installation in a different folder. Later I deleted that installation again, but the removal did not succeed completely. There are two folders remaining that I cannot get rid of: wpcf7_captcha and wpcf7_uploads (inside wp-content/uploads). Filezilla tells me: "550 Access is denied." but the folders (and files inside) have been set to writable.
How should I get rid of these folders? Everything else from that trial installation has already been removed. You will need to know that the site is hosted externally, on a Windows server with IIS.