Error in Creation of Purchase Requisition through LSMW

Hi

I am trying to craete a PR upload prog through LSMW batch input method. In the Specify File option I am giving the TXT file destination.The TXT file is saved at my desktop. But while saving it is givving an error as "No logical path has been specified", Message no. /SAPDMC/LSMW_OBJ_060046

If anyone can help me out.