creating a file and then copying it: how to break the dependency between the 2 steps in SSIS

you can fill data into file with SCRIPT COMPONENT AS DESTINATION.
then in the script component PostExecute method you can Flush and Close the streamwriter.

and you will never have problem on other tasks after this step.

for working with files in script component, you need to use System.IO.StreamWriter.
you should instanciate a new streamwriter at PreExecute method of script component
and fill values in flat file with streamWriter.WriteLine() in the ProcessInputRow

and finally close the stream writer in PostExecute method with
streamwriter.Flush();
streamwriter.Close();