Why are you mixing a SELECT with an INSERT and calling ExecuteNonQuery?
Start by streamlining your query:
string s = "INSERT INTO IP_Spools (RejectReason1,RejectReason2,RejectReason3) VALUES (@p1,@p2,@p3)";
And remove the fourth parameter - I suspect the error will go away because SpoolID is not a column in the RejReason table.