Problem with 1.2.18?

[Luke <..hidden..>]

My locality recently changed the rate of the most local sales taxes which 
apply to my company.

Specifically, I have:

State: 6%, order 1
City: 1%, order 1

I need now to have:

city: 2%

I entered a "valid to" date for the city's tax account and clicked 
update, and was given a new set of fields.

After entering the new tax rate for that account in the new set of fields 
(Thus filling in only the rate (%) field, and leaving the rest blank), I 
submitted, and got this:

"
   DBD::Pg::st execute failed: ERROR: invalid input syntax for integer: ""

Error!

   INSERT INTO tax (chart_id, rate, taxnumber, validto,
   pass, taxmodule_id)
   VALUES (?, ?, ?, ?, ?, ?)
   ERROR: invalid input syntax for integer: ""
"

Okay, I forgot the "order" value, so I set that to "1", which was the 
value in the original rule, and submitted again.  this time I got:

"
   DBD::Pg::st execute failed: ERROR: duplicate key value violates unique
   constraint "tax_pkey"

Error!

   INSERT INTO tax (chart_id, rate, taxnumber, validto,
   pass, taxmodule_id)
   VALUES (?, ?, ?, ?, ?, ?)
   ERROR: duplicate key value violates unique constraint "tax_pkey"
"

Lastly, I tried changing the "1" to a "2" in the order field of the new 
rule.  I Get:

"
   DBD::Pg::st execute failed: ERROR: duplicate key value violates unique
   constraint "tax_pkey"

Error!

   INSERT INTO tax (chart_id, rate, taxnumber, validto,
   pass, taxmodule_id)
   VALUES (?, ?, ?, ?, ?, ?)
   ERROR: duplicate key value violates unique constraint "tax_pkey"
"

What am I screwing up here, or is this a result of my first screwup?

Thanks

Luke