Ohhhhhhhhhhh OK i see the problem now. You're missing an equals sign:
<input type="hidden" name="txtStockId" VALUE="<%Request.QueryString("StockId")%>">
should be:
<input type="hidden" name="txtStockId" VALUE="<%=Request.QueryString("StockId")%>">
Man, I can't believe I didn't catch that.... ;)
HTH,
Snib
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