I received an error working in as .ascx file (haven't seen the error in other filetypes - yet) notifying me that an extension caused the erorr. As instructed by the message box, I turned on VS logging to ActivityLog.xml and here is the error I received in the log:

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index at System.ThrowHelper.ThrowArgumentOutOfRangeException() at System.Collections.Generic.List1.get_Item(Int32 index) at System.Collections.ObjectModel.ReadOnlyCollection1.System.Collections.Generic.IList<T>.get_Item(Int32 index) at Artem.VisualStudio.Outlining.OutliningTagger.CalculateChange(TextContentChangedEventArgs e) at Artem.VisualStudio.Outlining.OutliningTagger.HandleBufferChanged(Object sender, TextContentChangedEventArgs e) at Microsoft.VisualStudio.Text.Utilities.GuardedOperations.RaiseEvent[TArgs](Object sender, EventHandler`1 eventHandlers, TArgs args)

    /// <summary>
    /// Calculates the change.
    /// </summary>
    /// <param name="e">The <see cref="Microsoft.VisualStudio.Text.TextContentChangedEventArgs"/> instance containing the event data.</param>
    protected virtual void CalculateChange(TextContentChangedEventArgs e) {

        // full refactoring is in progress, then no need to calculate
        if (this.FullRefactoring) return;

        // changes are more than 1, then set full refactor state
        if (e.Changes.Count > 1) {
            this.FullRefactoring = true;
            return;
        }

        ITextChange textChange = e.Changes[0];
        ....