There is a huge problem in your code, it is 'SQL Injection" :
OleDbDataAdapter SQLAdapter = new OleDbDataAdapter("insert into tblproducts([pname],[pprice],[pselprice],[pcatid],[psubid],[psize],[pmaterial],[pcolor],[pdimension],[pitemweight],[pmaxweight],[pdescription],[pproductdetails],[freedelivery],[30dayreturn],[cod]) values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + DropDownList1.SelectedItem.Value + "','" + DropDownList2.SelectedItem.Value + "','" + DropDownList3.SelectedItem.Value + "','" + TextBox7.Text + "','" + TextBox8.Text + "','" + TextBox9.Text + "','" + TextBox10.Text + "','" + TextBox11.Text + "','" + TextBox12.Text + "','" + TextBox13.Text + "','" + DropDownList4.SelectedItem.Value + "','" + DropDownList5.SelectedItem.Value + "','" + DropDownList6.SelectedItem.Value+ "')", con);
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[
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SQL Injection[
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SQL Injection Attacks by Example[
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PHP: SQL Injection - Manual[
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How can I explain SQL injection without technical jargon? - Information Security Stack Exchange[
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