Can't upload files -- anyone else having problem

Last couple of days I am having problems uploading files.
I get through the selection process OK, but then a fleeting window comes up -- "Error, can't upload file, ...invalid path -- try again later" or something close to this.

Load is from Mac OS Catalina. Also tried from High Sierra -- identical problem.

Have done this many times before and don't think I'm doing anything different, but of course could be.

Anyone else experiencing this? Perhaps know of workaround? This is on project critical path.

Thanks.

Paul