This can be a problem with corrupted cookies that are send to a server.

Clear the cache and the cookies from sites that cause problems.

• "Clear the Cache": Edit > Preferences > Advanced > Network > Offline Storage (Cache): "Clear Now"
• "Remove the Cookies" from sites causing problems: Edit > Preferences > Privacy > Cookies: "Show Cookies"

I set the browser to clear cookies on closing. This was confirmed by having to log into accounts where cookies would normally 'remember' my login. I still got 'bad verb' errors. Therefore, I don't think bad cookies are entirely to blame. Also, the pages usually load successfully on the second or third attempt.