error while importing the graphmlz file...
Start tag expected, '<' not found in file:/C:/xampp/htdocs/myapp/protected/runtime/ProblemSolving.graphmlz, line: 1
Well, according to the short tutorial video I found on the Yii site, Yii supports importing *.graphml files while you are trying to import a *.graphmlz file.
That said, please ask future Yii questions in the Yii forum.