I had an issue with my phone where I could not open any sms messages I received on my phone. My sms settings was set up to use my memory card as the storage location. 
When I changed Memory in use to my Phone memory then any messages I receive I can open, but when I set it back to my memory card it doesn’t work.
So I done a bit of research and I found the path where my sms’s are stored on my memory card. The location is <MemoryCard>:\Private\1000484b. I figured that the best way to fix my problem is to delete this folder so that my memory database on my phone is reset (since this is what is causing the problem)
Now to do this you need to change your memory in use settings back to phone memory and open up the files in a file explorer or file manager (if you have trouble with this leave a comment), then delete that folder. Note: that will delete all sms messages on your memory card too.
Change the memory in use again setting in your messages and test to see if you can open messages again.
It worked for me.. I hope it works for you too =)
This should work on all Symbian 3rd Edition phones.