Silverlight control locked in runtime

I have a online survey running in Silverlight. Out of more than 1000 onetime users, there are thre开发者_如何转开发e users than cannot open a combobox on the first page. The control seems disabled and don't react on mouseclick.

Since it is one-time user, they don't wan't to help me with debugging and I cannot reproduce the problem myself.

Any ideas why 1000 users have no problem, and 3 are experiencing all controls like they were disabled?

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Jake, it would be hard to tell if the users aren't giving you any type of information like OS/Browser, screenshots, etc. I don't think there would be a general reason especially since you said yourself that 3 out of 1000 had the problem.