I had the same problem and I found a Microsoft support page that helped tramendously. Best of luck Doug,
*From URL at Microsoft Support website*
*SYMPTOMS
When you attempt to use the Out of Office Assistant, you receive the following error messages:
-The Out of Office assistant cannot be displayed.
-The client operation failed.
*CAUSE
Out of Office Assistant creates a set of two rules in the Inbox subtree. The first contains a Message Class of IPM.Note.Rules.Oof.Template.MicrosoftMessage with a field, PT_String8=MSFT:TDX OOF Rules. The other rule contains a Message Class of IPM.Note.Rules.OoFTemplate.Microsoft. One or both of these rules are corrupted or are not synchronized with the OOF-enabled indicator.
*RESOLUTION
Use the Mdbvue32 utility from the Exchange Server 5.5 CD-ROM or the Exchange Server 5.0 Resource Kit to delete the two entries for Out of Office.
1.Start Mdbvu32.exe.
2.Click MAPI_EXPLICIT_PROFILE, and then click OK.
3.Click the MAPI profile for the mailbox that you want to correct.
4.From the MDB menu, click Open Message Store.
5.Click Mailbox - username in the list, and then click Open.
6.On the MDB menu, click Open Root Folder.
7.Under Child Folders, double-click Top of Information Store.
8.Under Child Folders, double-click Inbox.
9.Examine each row of entries that appear under Associated Messages in Fld by double-clicking the CB items one at a time. You are looking for two items that have the following message properties:
The item that contains a message property Ox65EB that displays OOF Rules.
The items that contain a message property PR_MESSAGE_CLASS that displays IPM.Note.Rules.OofTemplate.Microsoft.
These are your Out of Office Assistant rules and your Out of Office Assistant template. Both must be removed by using steps 10 through 14.
10. Select both CB: values.
To do so, press and hold down CTRL while you click both CB values under Associated Messages in Fld.
11 In the Operations Available list, click lpFld-> DeleteMessages in the messages that are selected.
12.Click Call Function, and then click OK.
13.In the MAPI_FOLDER Inbox => Delete Messages dialog box, click OK.
14.Continue to close the dialog boxes, and then quit the Mdbvue32 utility. You must now reset the Out of Office message that you want in Outlook.