What if file is being written to but Exists for Check Whether File Exists

I'm trying to use the .....

Check Whether File Exists - new File( pathToFile ).exists()

.... to import after a file is created. The problem is the other program is still writing to the file so I don't get all the records.

Any ideas on how to keep it from importing until the other program is done?

Practical example:

Printing postage with Endecia...

Script:

Print Postage....

Loop

set variable [$$file_exists ; value:CheckWhetherFileExists( "C:\folder\Data-output.xml" )

exit loop if [$$file_exists = 1]

pause/resume 5 seconds

End Loop

I thought about continuing the loop until all records come back but that wont work if 1 address is invalid................