binding values to sql statement in DBI perl

Hi,

  I am having trouble with binding values to SQL statements using dbi perl.

The scenerio is as follows :

I have a scheduling database that holds the listings of classes and
there schedules for a university. I am trying to query the database to
display the listings of classes , sections for  a particular semester
that the user enters.
I am able to get the results with the actual value but then when I use
the variable which holds the values of the semester the user entered
and try querying , it displays an error message saying

"unbound place holder "

I am not sure of how to deal with this , I have tried different
combinations but in vain. Any input on this will be appreciated.

Deepblues