Error Message (Windows 98SE, Office 2000 Professional)

[wwob]

How do I get rid of this Microsoft Outlook error message?
"The custom form could not be opened. Outlook will use an Outlook form instead. The form required to view this message could not be displayed. Contact your administrator". I'm not part of a network, don't have an administrator, and never created a custom form.
This just came up this afternoon after I opened a gif attachment to an email. The message comes up anytime I try to open one of my contacts. I click it and the contact opens just like always. I tried deleting the email and its gif attachment but the error message still comes up.

[Leif]

Try these:

Q251415 OL2000: Custom Form Produces Error Message and Does Not Load

A search on Google using the reported error throws up many results, most of which suggest installing SR1.

[wwob]

I double checked. SR1 and 1a are installed.
The error message started coming up after I made changes in USERS. The error message comes up for some of the contacts but not all of the contact. It looks like the error message happens when I have written something in the bitg white box below the contacts name, address, and phone number.
I don't know what changes I made in USERS. Previously I wasn't aware there were any users on my machine. I'm the only one who uses it.