The Forms Cache

No Outlook discussion would be complete without mention of the dreaded forms cache. If you have never run into the issue I am about to describe, you will. Sometimes when your users attempt to open your form, they will get a message stating that the form could not be opened and that Outlook will use the standard form for that type of message instead. Most times, this problem is caused by forms cache corruption.

The forms cache is a local file system folder that, as its name implies, caches forms. Outlook uses the forms cache to minimize round-trips to the server if the form has not changed. The nice thing about the forms cache is that it automatically updates itself with the latest version of a form. You can usually find the physical folder in your file system that contains the forms cache by searching for the file frmcache.dat. This file is included in the folder to prevent multiple instances of a form from being cached.

This is one of the problems with the forms cache. Only single versions of the form can be cached. So if you publish your form to multiple form libraries, such as a folder form library and the Organizational Forms Library, the forms cache can easily get corrupted. You should therefore avoid publishing the same form to multiple forms libraries.

The second problem with the forms cache is that by default, the size for the cache is 2048 KB. This means that if you have a huge form (and I hope you do not build forms that big), Outlook will not be able to cache the form.

If you do run into weird errors in Outlook with your forms, you should clear the forms cache. You can delete all the files except frmcache.dat in the file folder, and Outlook will automatically download new copies of the forms. However, Outlook 2002 offers an even easier way to clear the forms cache: directly in the Custom Forms dialog box. From the Tools menu, choose Options. In the Options dialog box, click on the Other tab and then click the Advanced Options button. In the Advanced Options dialog box, click the Custom Forms button. In the resulting dialog box, click the Manage Forms button. In the Manage Forms dialog box, click the Clear Cache button. Exit and restart Outlook. Clearing the cache will solve most of your form corruption problems.

However, if your problem was not solved and you were saving backups of your form as an .oft file, you can delete the form from the Exchange Server and then republish it. This should remove any corruption from the form. If this does not clear the corruption, you probably have bigger problems than just forms in your Outlook client.