try with
string quer = "insert into Table1([Invoice Number],Date,Product,[Serail Number],Status, Amount) Select Top(1) [Invoice Number],Date,Product,[Serail Number],Status, Amount from Inventory where Product='" + TextBox10.Text + "'";
you need may need to specify the column names and "from" keyword in the second part of the sql select statement. baically syntax would be
INSERT INTO table1 (column names....)
SELECT TOP (1) column names....
FROM table2
INSERT TOP (1) INTO table1 (column names....)
SELECT column names....
FROM table2
you better use parameterized sql statement rather than concatenating strings to avoid sql injection attacks.