if you have same name of column in collection and in grid when you filter it you will get one my sql error
SQLSTATE[23000]: Integrity constraint violation: 1052 Column ‘status’ in where clause is ambiguous at that time in grid _prepareColumns() funtion
add filter_index option in fields that is
$this->addColumn("status", array(
"header" => Mage::helper("custompromotion") ->__("Status"),
"align" =>"left",
"index" => "status",
"filter_index" => "main_table.status",
'type' => 'options',
'options' => $option, ));
“filter_index” =>; “main_table.status”,
main_table.status==> “main_table” is alias of you table and “status” is column
this issue will happen when you join 2 tables and have same field name
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