Insert blocks from a txt file lisp PROBLEM

Hi if anyone could help I would appreciate it.
I work in a Staduim that has a lot of touring rock shows. When we get
their lighting rig info we have to check wether it will pull the roof
down or not. Lighting pionts for shows are supplied as list of x y
coords, names and weights. I have wriiten a LISP routine to insert
atrributed blocks from the list on a .txt file. The txt file is list is
formated:

L1 1800 -22.5 41
L2 1800 -8.5 41
L6 700 0 21

I use this routine to insert the blocks (I wrote it myself and am no
expert)but it sometimes has some random results and I cant figure out
why. The routine works but some of the pionts xy insert coordinates are
wrong. Please look at it and help. Also feel free to use it if you
like, remember to take all spaces out of the txt file before you go
though and it is slightly faulty.

(defun inpt ()
(command "insert" "Point" ptt "" "" "" ptname ptw )
);I think this bit is a bit dodgy again no expert

(Defun C:IMPRT4 (/ nme txt dt ptt ptname ptw)
(setq nme (getstring "\nName of text file to import: "))
(setq nme (strcat "T://1.Rod Laver Arena//Data//" nme ".txt"))
(setq txt (open nme "r"))
(setq dt (read-line txt))
(split_tab_delimited_str dt); this function splits the tab delimited
string into a list of strings post me if you want it

(setq ptname (car dt))
(setq ptw (cadr dt)
);setq as long as the weight is in kg otherwise I do like below to
convert it

(setq ptt
(list
(cvunit (distof (nth 2 dt) 2) "feet" "Millimeters")
(cvunit (distof (nth 3 dt) 2) "feet" "Millimeters")
); list converts xy coordinates from decimal feet to mm
); setq

(inpt)

(while (/= dt nil)
(setq dt (read-line txt)) (split_tab_delimited_str dt)

(setq ptname (car dt))

(setq ptw (cadr dt)
);setq

(setq ptt
(list
(cvunit (distof (nth 2 dt) 2) "feet" "Millimeters")
(cvunit (distof (nth 3 dt) 2) "feet" "Millimeters")
); list
); setq

(inpt)

); close while

(close txt)
(command "redraw")

); Inserts pionts from text file


Thanks
Justin