I have clients on 12.1 who are getting this pop-up:

"Outlook experienced a serious problem with the Symantec Endpoint Protection Outlook add-in" add-in. If you have seen this message multiple times, you should disable this add-in and check tko see if an update is available. Do you want to disable this add-in?"

So, I don't want to disable the SEP Outlook add-in because that's a layer of protection I want to keep, but how do I keep this add-in from erroring out on me?

Try this once

Delete the file C:\Documents and Settings\%username%\Local Settings\Application Data\Microsoft\Outlook\extend.dat and allow the file to be re-created when Outlook is started

Are you usung outlook 2010? If yes have a look at this KB

Support for Symantec Endpoint Protection's Optional Outlook Plug-In on Outlook 2010

AravindKM, thanks for the article.

The clients are on Outlook 2010, but the last part of the article reads "The SEP 12.1 Outlook plug-in is supported for Microsoft Outlook 2010 on both 32 and 64 bit versions" so these clients should not be receiving these errors.

Which is the version of SEP client?

If you disable SEP outlook add-in whether the problem is getting resolved?

The clients I have seen are at least 12.1 RTM.

Yes, of course, if I disable the add-in the issue goes away, but like I said, I want this layer of protection.

Can you try to upgarde one or two clients to SEP 12.1 RU1 MP1 and try?

Well, yeah, but you can propose that as a solution for all issues on clients that are not on MP1. I might as well do that first before posting anything or contacting support if that's the only solution you have.

I am not able to find any other solutions