I am using Sharepoint 2010 and Visual Studio 2010 to create custom webpart that show me data from list in tree view, the data is text items. When I put the tree view it show me the data but the expand and collapse options not working, when I click the "+" or "-" to expand or collapse it show me JS error:

Message: 'ctl00_m_g_b501a2fe_3a51_47b1_9aa2_15bd7b7f1e8a_ctl03_Data' is undefined



Any Help ????