Uploading a generated file – results in "file not found"

I have a:

send (to save a csv output to file),

followed by a send (to call a WS, that uploads the file to DB).

—

some times the WS cannot find the file.

Given that BTS is combining the two sends into one persistence point what is the appropriate way to ensure the “save” is completed before WS tries to upload the file?

Regards

Bibhakar Saran