Hi Ramesh,
This is a known limitation with query browser on bex query.
If we have a BW variable as well as a prompt defined at the dashboards level then we have an issue in binding to excel and is grayed out.
Either we can have filtering done at BW or at Dashboards level but not at both.
Please check KBA
2103395 - BW variable greyed out in the query browser in
Dashboard
Amit