[THIN] SSL errors

I just wanted to confirm a couple of things that I have been thinking...
Generally during a given week, we will have one or two users that spend the day getting the "unable to establish a connection to the Citrix SSL server, the SSL erver you have selected is not accepting connections"
Since it is almost never more then one or two users out of the almost 1200 we have logging in at peak times I am certain it is not a failure on our end. If I remember correctly, if the DNS does not resolve properly for the SSL connection that error will occur.
It also generally goes away within 24 hours. This makes me think it is an issue with the client's DNS resolution.  Are there any simple steps I can take aside from waiting to try and correct this issue?  With our clients most all of them have no access to anything beyond their PC (no ability to modify or play with their network settings.
We have a very heterogenous client base, most of them being back office PCs at hotels so the users are very limited in their knowledge and have limited IT resources at their disposal.
We are running PS 4.5 and WI4 on W2k3 servers.