Problems with Mail after upgrading to MAC OS10 version 10.6.8

I upgraded to MAC OS10 version 10.6.8 about ten days ago, and have since had lots of problems with mail. Since I upgraded, I have downloaded several software updates, including one for improving the general softeware system of Leopard. Since this morning, I no longer have the Mail icon in the dock and when I try to open it in Applications a window comes up saying:

'You can't use this version of Mail with this version of Mac OS X. You have Mail version 4.5 (1084/1085). It can't be used on Mac OS X Version 10.6.8 (Build 10K549)

Can I download a version that I can use with this Mac, and can anybody give me the site where I can find this. I have tried without success