List stage file errors out OIC - Assign Operation Empty result set

Hi experts,

In the integration - for each source file based on a document type of each source record I will generate 2 kinds of .csv file in staging area and once after all the records are proccessed I will list them in staging area.

In case of multiple files, always the first file goes fine without any error while the second file will error out at listing the files in staging area  with below error message.

"Assign Operation Empty result set. /n The to-spec does not yield any data; the remove operation cannot be performed. /n The operation named in the error message was not performed because to-spec did not yield any data. /n Verify the to-spec of the assign activity at line number 29902 in the BPEL source. /n  /n