Perhaps you are referring to McAfee Anti-Spam extension? If so, that addon has been disabled because it is causing crashes for users of newer Thunderbird 52 release

I think this involves sending email from a document-scanning program, i.e. it is a MAPI problem in Windows 7. There are a couple of methods mentioned here that amount to repairing the MAPI configuration.

Thanks Steve, that makes perfect sense. https://support.mozilla.org/en-US/questions/1158852 is another one.

https://bugzilla.mozilla.org/buglist.cgi?j_top=OR&list_id=13568992&o1=substring&o2=substring&chfieldfrom=2017-04-01&v1=mapi&v2=mapi&f1=component&chfieldto=Now&query_format=advanced&f2=short_desc&product=MailNews%20Core&product=Thunderbird are recent bug report activity

There appear to be several proposals to work around this problem in TB 52, some work, some don't, but it looks like downgrading to TB 45 in the meantime is worthwhile if this is a critical feature.

thanks for your input. Windows has identified that one of my USB connections is faulty. I suspect it is the USB from the printer.