fix for issue #2500

lib/less/contexts.js

@@ -57,6 +57,8 @@ var evalCopyProperties = [
 contexts.Eval = function(options, frames) {
     copyFromOriginal(options, this, evalCopyProperties);
 
+    if (typeof this.paths === "string") { this.paths = [this.paths]; }
+
     this.frames = frames || [];
     this.importantScope = this.importantScope || [];
 };