Cannot forward emails

Cannot forward emails. I can send and receive emails normally. "Send Message Error Sending of the message failed. Unable to open the temporary file C:\users\Ed\AppData\Local\Temp\nsmall.tmp. Check your Temporary Directory' setting." OS Win7 Ultra-64bit Immunet 6.2.4.10819 & MS Security Essentials Thunderbird 60.3.3 (32-bit) "You are currently on the release update channel." Based on the error msg., I created a 0 byte file "C: \users\Ed\AppDatat\Local\Temp\nsmall.tmp" using NOTEPAD++. I was able to forward one email but subsequent attempts failed. Same error msg. but "nsmail.tmp" was modified to "nsmail-1.tmp". Renamed file to "nsmail-1.tmp"to no avail, this time the file was amended back to "nsmail.tmp" I have no idea what to try next.