This is more of sql server question. I hope it is ok in this forum.
I am attempting to modify the structure of a sql server table in enterprise manager. Whenever i attempt to add a field, any field, and click save, I get the message:

'Unable to preserve trigger arinvc_update. Invalid column name 'R'

I don't have a column named 'R'.

This is an existing database, with existing stored procedures and triggers (I didn't write them) that I need to maintain/update.

The stored procedure in question is as follows:

/** ID: AR50048.01 Name: arinvc_update Owner: AM ScriptDate: 03/20/2000 **/
create trigger arinvc_update ON dbo.arinvc
for update
as
begin
if exists (select lexcl from cosyst where lexcl = 1) /* exclusive mode */
return
declare @lcuid char(15), @lnsalesamt numeric(16, 2), @lndiscamt numeric(16, 2),

@lnbalance numeric(16, 2), @lctype char(1), @lnvoid smallint, @lcinvcuid char(15),
@lcpaycode char(10), @lccardno char(20), @lcexpdate char(5), @lccardname char(30),
@lccustno char(10), @lnatdsamt numeric(16, 4), @lcinvno char(10), @lnpaytype integer
declare curarinvc_upd scroll cursor for select nsalesamt, ndiscamt, nbalance,
ctype, lvoid, cuid, ccardno, cpaycode, cexpdate, ccardname, ccustno, cinvno
from inserted
open curarinvc_upd
fetch next from curarinvc_upd into @lnsalesamt, @lndiscamt, @lnbalance,
@lctype, @lnvoid, @lcinvcuid, @lccardno, @lcpaycode, @lcexpdate, @lccardname,
@lccustno, @lcinvno
while @@fetch_status <> -1
begin

if @@fetch_status = -2
begin
fetch next from curarinvc_upd into @lnsalesamt, @lndiscamt, @lnbalance,
@lctype, @lnvoid, @lcinvcuid, @lccardno, @lcpaycode, @lcexpdate, @lccardname,
@lccustno, @lcinvno
continue
end
if @lnvoid = 1
begin
update arinvc
set nfsalesamt = 0, nfdiscamt = 0, nftaxable1 = 0, nftaxable2 = 0,
nffrtamt = 0, nftaxamt1 = 0, nftaxamt2 = 0, nftaxamt3 = 0, nfadjamt = 0,
nffinamt = 0, nfbalance = 0, ntaxable1 = 0, ntaxable2 = 0, nsalesamt = 0,
ndiscamt =0, nfrtamt = 0, nfinamt = 0, ntaxamt1 = 0, ntaxamt2 = 0, ntaxamt3 = 0,
nadjamt = 0, nbalance = 0
where cuid = @lcinvcuid

end

update arinvc set nfbalance = ((nfsalesamt -nfdiscamt) + nffrtamt + nffinamt +
nftaxamt1 + nftaxamt2 + nftaxamt3 + nfadjamt) - ( nftotpaid + nftotdisc + nftotadj +
nftotdebt), nbalance = ((nsalesamt -ndiscamt) + nfrtamt + nfinamt + ntaxamt1 +
ntaxamt2 + ntaxamt3 + nadjamt) - ( ntotpaid + ntotdisc + ntotadj + ntotdebt + ntotmcvar +
nmcround) where cuid = @lcinvcuid

update arinvc set nmcround = nbalance, nbalance = 0 where nfbalance = 0
and cuid = @lcinvcuid

update arcust
set arcust.natdsamt = arcust.natdsamt - (select nsalesamt - ndiscamt from deleted

where ccustno = arcust.ccustno and cuid = @lcinvcuid) +
(select nsalesamt-ndiscamt from arinvc

where ccustno = arcust.ccustno and cuid = @lcinvcuid ),
arcust.nbalance = arcust.nbalance - (select nbalance from deleted where ccustno

= arcust.ccustno and cuid = @lcinvcuid) +

(select nbalance from arinvc where ccustno = arcust.ccustno and cuid = @lcinvcuid)
where arcust.ccustno = @lccustno
if @lctype = "R"
update arcust
set arcust.nopencr = arcust.nopencr + (select nbalance from deleted where
ccustno = arcust.ccustno and cuid = @lcinvcuid) -
(select nbalance from arinvc where ccustno = arcust.ccustno

and cuid = @lcinvcuid )
where arcust.ccustno = @lccustno

select @lnpaytype = (select npaytype from arpycd where cpaycode = @lcpaycode)
if @lnpaytype <> 2
update arinvc set cchkno = '' where cuid = @lcinvcuid

if @lnpaytype <> 3
update arinvc set ccardno = '' where cuid = @lcinvcuid


if @lnpaytype = 5
update arinvc set ntermdisc = (select ntermdisc from arpycd where
cpaycode = arinvc.cpaycode), ndiscday = (select ndiscday from arpycd where
cpaycode = arinvc.cpaycode), ndueday = (select ndueday from arpycd where
cpaycode = arinvc.cpaycode) where cuid = @lcinvcuid
else
update arinvc set ntermdisc = 0, ndiscday = 0, ndueday = 0
where cuid = @lcinvcuid


if @lnvoid = 0 and @lccardno <> ''
begin

if not exists(select arcard.ccardno from arcard where

arcard.ccustno = @lccustno and arcard.cpaycode = @lcpaycode and
arcard.ccardno = @lccardno)
begin
execute vsp_am_assignuid @cretvalue = @lcuid output, @bfromfront = 0
insert into arcard(cuid, ccustno, cpaycode, ccardno)
values( @lcuid, @lccustno, @lcpaycode, @lccardno)
end
update arcard set cexpdate = @lcexpdate,
ccardname = @lccardname where ccardno = @lccardno
end
fetch next from curarinvc_upd into @lnsalesamt, @lndiscamt, @lnbalance,
@lctype, @lnvoid, @lcinvcuid, @lccardno, @lcpaycode, @lcexpdate,
@lccardname, @lccustno, @lcinvno
end

close curarinvc_upd
deallocate curarinvc_upd
end

Can anyone explain this message?

TIA