don't understand error

[purple]

I'm getting the following error:
Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\view_users.php on line 121
What does this mean?
Here is the bit of code that's causing it apparently.

$bg = "#eeeeee";

while($row = mysql_fetch_array($result, MYSQL_ASSOC))
{
	$bg = ($bg=='#eeeeee' ? '#ffffff' : '#eeeeee');
	echo '<tr bgcolor="' . $bg . '">
		  <td align="left"><a href="edit_user.php?id=' . $row['user_id'] . '">Edit</a></td>
		  <td align="left"><a href="delete_user.php?id=' . $row['user_id'] . '">Delete</a></td>
		  <td align="left">' . $row['last_name'] . '</td>
		  <td align="left">' . $row['first_name'] . '</td>
		  <td align="left">' . $row['dr'] . '</td>
		  </tr>';

[dagon]

$result is not a valid resource (the mysql query failed)

[purple]

what could have caused a query to fail?

[bradgrafelman]

Invalid SQL syntax.

Use standard debugging techniques to figure out why. For example:

$query = "SELECT foo FROM bar";
$exec = mysql_query($query) or die("SQL error: " . mysql_error() . "<br>Query: $query");