Im****t from csv file works fine , but not in multi user env.

Hello,

I have a front-end db and back-end db. The FE im****ts csv files into
tables. 
This works fine but if more than one user tries to im****t the files then
only 
the first gets all data. How to manage this for multi user or catch this
with 
message "currently in use, try later".??

thx
juvi