I went to your form and filled it out (it looked clean when I got there). I sent a test message, and the error messages appeared. I tried again, but when I refreshed the page, my name (neilo) was still in the 'name' field.
I closed the browser window, cleared my cache /*edit: But not the cookies */ and went back to your contact form page. My name was still in the 'name' field. and the error messages were still displaying.
I have no idea how that could happen, unless it is somehow being cached on your server, or the session error is being written to a cookie (is that possible? Is that even a thing?)
The same thing seems to be happening with two PowerStore Installations (one resolved - maybe) where there is an initial problem with file upload validation, but the error is being 'stored' and persists thereafter (even though the files are being uploaded fine without you knowing it unless you look in the server uploads folder).
I would try uploading your form page and the Spry Assets again (delete them off the server first and go to your contact page and refresh to make sure they've gone).
Edit: I initially just closed the FF Tab that the page was on, and cleared the cache. This time I closed down the actual browser, and the error messages went. But the form still fails on fields after the 'name' field (which isn't a validated field).
Edit 2: Yes - the cookie that stores the session id (PHPSESSID) is preventing me from refreshing the form and is making the errors stick until I close the browser. Sorry for the ramble, Diana.