The Offline Client toolbar is no longer available in Outlook 2007, possibly after installation of KB952142 from MS.
The Offline Client was not able to load due to the installation of KB952142, and was disabled.
Go into Outlook and then click on the tools drop down menu.
Go into Trust Center and click on Add Ins.
On the Add Ins page, select the Manager pull down list and select "Disabled Items".
Enable the Offline Client.