Problem using the customsource textbox

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C#

Hi friends, I am facing a problem using a customsource text box. I am getting some particular data from mysql table using a query and I am adding it to a textbox as custom source data in a c# project. The problem is, I can't use the down arrow button to select customsource data. If I set the property as:

textbox.AutoCompleteSource = AutoCompleteSource.None;

in the code it is working. I can't get the full data from db when I am typing next time. Can anybody give me the solution please?