Thank you so much for the replies.
I found the solution to the problem (well, I didn't find it!!)
I went onto fiverr.com and got a guy to fix it...its a great place to go if you ever have niggley little problems that you can't fix! And it obviously only cost me a fiver!
Anyway...this is how I fixed the problem:
Log into your blog.
Click on permalinks under the settings menu (on the lower left hand side of the screen).
I had chosen "custom structure" which looked like this..../%2011%/%postname%/
All you have to do is take the % from around "2011" so it should then look like this.../2011/%postname%/
And voila, it worked perfectly!
I hope this helps you in some way as its a very frustrating problem!
Thanks again for the replies, I really appreciate it.