John, thank you for bringing this to our attention.  I was able to successfully replicate the bug.  I have added to this our bugs list and will change this thread from a question to a problem and mark it was known.

 

In the meanwhile, go to System Adminn | Antispam Administration | Filtering tab and make sure that any of the spam probability actions with "Prefix subject with text" has a value in the "Text to Add" field.  If that field is blank, you will get the error you received.

John, can you set all of the override settings to no action, save, then change domain setting to use default settings, and save again?

Yeah! That got rid of the error, but brings up another question. So, when the domain was using custom settings and they also changed the weights; when you revert back to using the default settings shouldn't the weights revert back to the default values too? (Because in my case they are not reverting back to the defaults set in the System Admin section.) 

I know that if changes are made for other things, they would not automatically propagate; but it would seem that the SPAM values should. I mean isn't that what "Use Default Settings" implies? 

 

And regarding uploading an image, that picture button does not have that functionality. I can upload the file on my server and post a link to it to be viewed here, but I can't upload a file from my computer directly. And frankly, having to a. take a screen shot, b. having to upload it to the server then c. determine the url and finally click on your little picture icon and paste in the URL is--well a PITA. 

John, I noticed the settings not reverting to higher level defaults (domain to system or user to domain).  I've made a note of this in our bugs list as well.

Thanks. I also doesn't appear to be deleting weights if the RBL is no longer used. Glad it's now noted and on the list.