download the driver from here. I think 1.3.1 is the latest stable
stop openfire
located jtds.jar .. it should be in \Program Files (x86)\Openfire\lib
rename it to something like jtds.jar.old
From the zip you downloaded earlier, extract jtds-1.3.1.jar
copy it to \Program Files (x86)\Openfire\lib and rename it to jtds.jar
start openfire
You should now be running the current driver.