build number:2.6.0.v20100506-0630

steps to reproduce:
1. insert a data item, bind with dataset and name it "data"
2. insert a chart, use report item "data"
3. dnd column binding from data preview to set series

expected result:
step3 can be done

actual result:
fail to do so, but context menu can be used to set series
fixed. the dnd transfers the binding name. the expression is needed to check if valid.
2.6.0.v20100513-1121