Logs would work best...but, a few questions...
1) Is it integrated with AD?
2) When you say it's not "user specific", does this mean that the same user, using the same username/password/server location cannot connect from one spark client on the first machine, but can connect from another spark client on another machine? Your wording there confused me a tad.
Which leads to this...
3) Can ANY user log in on the offending spark client? Or does everyone who tries get the same error?