C# - DataReader Already Open When Using LINQ?

I've got a static class containing a static field which makes reference to a wrapper object of a DataContext.

The DataContext is basically generated by Visual Studio when we created a dbml file & contains methods for each of the stored procedures we have in the DB.

Our class basically has a bunch of static methods that fire off each of these stored proc methods & then returns an array based on a LINQ query.

Example:

public static TwoFieldBarData[] GetAgesReportData(string pct)
{
return DataContext
.BreakdownOfUsersByAge(Constants.USER_MEDICAL_PROFILE_KEY, pct)
.Select(x => new TwoFieldBarData(x.DisplayName, x.LeftValue, x.RightValue, x.TotalCount))
.ToArray();
}

Every now and then, we get the following error:

There is already an open DataReader associated with this Command which must be closed firs

This is happening intermittently and I'm curious as to what is going on. My guess is that when there's some lag between one method executing and the next one firing, it's locking up the DataContext and throwing the error.

Could this be a case for wrapping each of the DataContext LINQ calls in a lock(){} to obtain exclusivity to that type and ensure other requests are queued?