can't display the visual

Hi,

I have created a Gannt chart, and a table so when I select one of the bars on the chart it will show me the properties of the task in the table in detail. However, when I select SOME of the bars I receive this error message: 

Couldn't load the data for this visual

The query contains a filter with duplicate columns which are not allowed.

And the table displays a X and says "can't display the visual". 

I can't figure out what the issue is as some of the bars when selected show the information in the table no problem.

Please help. Thanks.

H