Help inserting into multiple tables

[ROCKINDANO]

I am working on a asset project to insert, delete and view assets (items) that i owe. I am having trouble in the insert part.

 

i have four tables

 

department (DeptID, DeptName) DeptID is the primary key in this table.

 

assetcategory (AssetCatID, AssestCategory) AssetCatID is the primary key in this table.

 

asset (AssetID, AssetDescription, EmpID, AssetCatID, DeptID, Model, Maker, SerialNUm, DateAguired) AssetID is the primary key here.

 

Employee (EmpID, FirstName, LastName) EmpID is the key here.

 

and this is the code i have to insert using php.

		<?php 
			if(isset($_POST['submit'])){

				$FirstName = mysql_real_escape_string($_POST["FirstName"]);
				$LastName = mysql_real_escape_string($_POST["LastName"]);
				$DeptName = mysql_real_escape_string($_POST["DeptName"]);
				$AssetCategory = mysql_real_escape_string($_POST["AssetCategory"]);
				$Model = mysql_real_escape_string($_POST["Model"]);
				$Maker = mysql_real_escape_string($_POST["Maker"]);
				$SerialNum = mysql_real_escape_string($_POST["SerialNum"]);
				$DateAguired = mysql_real_escape_string($_POST["DateAguired"]);
				$AssetDescription = mysql_real_escape_string($_POST["AssetDescription"]);
				$AssetCatID = mysql_real_escape_string($_POST["AssetCatID"]);
				$AssetID = mysql_real_escape_string($_POST["AssetID"]);
				$EmpID = mysql_real_escape_string($_POST["EmpID"]);
				$DeptID = mysql_real_escape_string($_POST["DeptID"]);

				if(empty($FirstName) || empty($LastName) || empty($DeptName) || empty($AssetCategory) || empty($Model) || empty($Maker) || empty($SerialNum) || empty($DateAguired) || empty($AssetDescription))
				{
					print "Please feel in all fields";
				}
				else
				{
				///insert into the department table..........
				$query1= "INSERT INTO department VALUES (null,'{$DeptName}')";
				$result1 = mysql_query($query1) or die(mysql_error());
				$DeptID = mysql_insert_id();

				//insert into the assetcategory table
				$query2= "INSERT INTO assetcategory VALUES (null,'{$AssetCategory}')";
				$result2 = mysql_query($query2) or die(mysql_error());
				$AssetCatID = mysql_insert_id();

				//insert into the assets table
				$query3= "INSERT INTO assets VALUES (null,'{$AssetDescription}', '{$EmpID}','{$AssetCatID}','{$DeptID}','{$Model}','{$Maker}','{$SerialNum}','{$DateAguired}')";
				$result3 = mysql_query($query3) or die(mysql_error());
				$AssetCatID = mysql_insert_id();


				print $query1;

				}



			}
			else {
		?>

 

the page is displaying this error: "Column 'AssetCatID' cannot be null"

 

I would need help in inserting into all table required data. any help? hope i am making sense