help with Array

I have a script which is used to randomly allocate a teaching slot to a teacher.

What it does it to initially select which teachers are free for a time slot

Then it counts how many are free for the time slot.

Then it uses the randomize routine below to randomly allocate the lesson to a teacher.

Since arrays start to count at zero, then I have to use the line below to reduce the count by 1

e.g. if the sql shows 'FREE_TCHR_CT' is 2, I have to reduce that to 1, so that the array can count from 0 to 1, instead of from 0 to 2, which will end up throwing out a fld_t value of nothing...

Anyway, most of the time this process works, but I occasionally get this error:

Microsoft VBScript runtime (0x800A0009)
Subscript out of range: 'lrandom'
/japan/users/save.asp, line 59

line 59 is:

t_id = myArray(lrandom)

I think this may only occur when FREE_TCHR_CT = 2

Can anyone suggest why this might be happening please?

Thanks

Jim

code below:

--------------------
sql002 = "SELECT fld_id, fld_t, (time_to_sec(fld_time)/1800) as periodnumber FROM appointments "
sql002 = sql002 & "where fld_date = '"&d&"' AND (time_to_sec(fld_time)/1800) = '"&t&"' AND fld_cat = 2 GROUP BY fld_id"

response.write "sql002<BR>" & sql002 & "<HR>"

set rs002 = oConn.Execute(sql002)

'since there are free teacher(s) count the number of free teachers

sql003 = "SELECT COUNT(fld_id) AS FREE_TCHR_CT FROM appointments where fld_date = '"&d&"' AND (time_to_sec(fld_time)/1800) = '"&t&"' AND fld_cat = 2 "
response.write sql003 & "<HR>"
set rs003 = oConn.Execute(sql003)
FREE_TCHR_CT = rs003("FREE_TCHR_CT")
response.write "FREE_TCHR_CT: " & FREE_TCHR_CT & "<BR>"

'if there is more than one teacher free then do the random thing

if FREE_TCHR_CT > 1 then

FREE_TCHR_CT = FREE_TCHR_CT-1
response.write "FREE_TCHR_CT rand: " & FREE_TCHR_CT & "<BR>"
rs003.Close:set rs003=nothing

'response.write "<br><br>FREE_TCHR_CT: " & FREE_TCHR_CT & "<hR>"

dim myArray
ReDim myArray(FREE_TCHR_CT)

randomize

x = 0
do while not rs002.eof
y = rs002("fld_id")

myArray(x) = rs002("fld_t")

x=x+1
rs002.MoveNext
Loop
rs002.close:set rs002 = nothing

upperbound=ubound(myArray)
lowerbound=0
lrandom = ((upperbound - lowerbound + 1) * rnd + lowerbound)

t_id = myArray(lrandom)

else

t_id = rs002("fld_t")

end if

response.write "<hr>t_id: " & t_id & "<HR>"
'response.write "row_id: " & row_id & "<HR>"