From the error:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'update (...
it looks like your table is called update
That's a reserved word in SQL, so it's generating an error.
If possible, you should rename the table, as using reserved words as table or column names is confusing; but if that's not feasible, you can escape the name with backticks; try this as your second SQL call:
INSERT INTO `$UPname` (tnumber2, pdate, act, paddress, up) VALUES('$tnumber2','$pdate','$act','$paddress','$up')");
I'll also add the compulsory warning that mysql_ functions are deprecated, and you should switch to mysqli_ or PDO - they both help you write safer code. Also, if you're going to be using variables for table names, you need to be make sure that you're validating them very, very well.