Web Essentials 2015 with SCSS file

[MarkSky]

Today, when I wrote the SCSS file.
Visual Studio 2015 showed me there is an error happened.
And I see ActivityLog.xml, it showed:

<entry>
   <record>1053</record>
   <time>2016/11/09 06:35:28.779</time>
   <type>Error</type>
   <source>Editor or Editor Extension</source>
   <description>System.ArgumentOutOfRangeException: &#x7D22;&#x5F15;&#x548C;&#x9577;&#x5EA6;&#x5FC5;&#x9808;&#x53C3;&#x8003;&#x5B57;&#x4E32;&#x4E2D;&#x7684;&#x4F4D;&#x7F6E;&#x3002;&#x000D;&#x000A;&#x53C3;&#x6578;&#x540D;&#x7A31;: length&#x000D;&#x000A;   &#x65BC; System.String.Substring(Int32 startIndex, Int32 length)&#x000D;&#x000A;   &#x65BC; Microsoft.CSS.Core.Text.StringTextProvider.Substring(Int32 start, Int32 length)&#x000D;&#x000A;   &#x65BC; Microsoft.CSS.Core.Text.TextRange.GetText(ITextProvider textProvider)&#x000D;&#x000A;   &#x65BC; Microsoft.CSS.Core.Parser.ParseItem.get_Text()&#x000D;&#x000A;   &#x65BC; MadsKristensen.EditorExtensions.Css.VendorClassifier.&lt;&gt;c__DisplayClass7_0.&lt;GetClassificationSpans&gt;b__0(Declaration d) &#x65BC; C:\projects\webessentials2015\EditorExtensions\CSS\Classify\VendorClassifier.cs: &#x884C; 72&#x000D;&#x000A;   &#x65BC; System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()&#x000D;&#x000A;   &#x65BC; MadsKristensen.EditorExtensions.Css.VendorClassifier.GetClassificationSpans(SnapshotSpan span) &#x65BC; C:\projects\webessentials2015\EditorExtensions\CSS\Classify\VendorClassifier.cs: &#x884C; 72&#x000D;&#x000A;   &#x65BC; Microsoft.VisualStudio.Text.Classification.Implementation.ClassifierTagger.&lt;GetTags&gt;d__5.MoveNext()&#x000D;&#x000A;   &#x65BC; Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.&lt;GetTagsForBuffer&gt;d__38.MoveNext()</description>
 </entry>

I would like to know what's wrong.