Exchange 2010 SP3 Update Rollup 8
Earlier on this month Microsoft released Update Rollup 8 for Exchange 2010 SP3.
Unfortunately this update has caused issues with Outlook syncing with Exchange. (This does not affect Activesync, OWA, POP etc)
If you are receiving the “Cannot Open Item” error message and you have this update installed, uninstall it and roll it back to the to Update Rollup 7.
In due course, Microsoft will release Update Rollup 8 which will replace the dodgy update.
There’s more information on the Exchange Releases website.