typeset -l var2=$var1

I have a korn shell script that has been working fine -- until someone tried to use it on a server and got the following error on a typeset -l command:

Enter environment (cert or prod) [cert]:
rman.dbsetup.ksh: line 453: typeset: -l: invalid option
typeset: usage: typeset [-afFirtx] [-p] name[=value] ...

...which seems to say that "typeset -l" (for translating to lower case) does not work on some linux korn shell implementations. Does anyone (a) know why this is happening and (b) have a translation to lower case that works on all implementations of KORN shell/linux (I have man y other places that use "typeset -l" that are not included in the code supplied here, so the need is for a general utility to translate to lower case).

Thanks!

msg "\n\n\nEnter environment (cert or prod) [${default}]:"
 read copr
 typeset -l cop=$copr
 
 if [ ! "$cop" ]
 then
       cop=$default
       loop=""
       break
 fi

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