The error is occuring because the query dispatcher expects the path to the tcl script is not under the 'packages' directory. This same error will also occur, if you didn't declare your tcl proc using ad_proc. How is your proc declared, and where is it located in the file-system relative to the openacs installation?
Ugh, I should have proofread that last one. I meant to say: "The error is occuring because the query dispatcher expects the path to the tcl script to be under the packages directory."