This time, I don't know what the problem is, as I have the latest version of both electrum and coldcard. Does anybody have experience with this?
Did you update either Electrum or the coldcard firmware since you last attempted to send a transaction and/or had the same issue? 
If so, it's possible that one of them has introduced an issue...Not sure if you can downgrade the Coldcard... but using an older version of Electrum is relatively easy (you can grab one of the portable versions if you're using Windows and use it temporarily until you resolve the problem). The only issue you may run into is if the Electrum wallet file version has been "upgraded", then a lower version of Electrum will likely refuse to open it... and you'll have to re-import the watching only wallet into Electrum.
