Err with scheduling an abap program using open dataset

Question

issue: have an abap program which uses "open dataset ... for input ..." to read the file. 
- with manual ly running it, receive the following message "dataset_not_open".  
- with scheduling it, receive same message
attempting to run an abap program as part of a process chain (ie scheduling a background job) in BI.
the abap performs the following fxns:
1) read a file on the server
2) removes delimiter, renames it
3) rewrites the file onto the server
initially used ws_upload for reading and ws_download for writing the file. 
- both fxns worked fine if it is run manually --> but failed as a  background (part of process chain)
- note 7925 states can't use ws_upload, download for background jobs
-so switched to "open dataset"
Any suggestions as to why the "open dataset" does not work is greatly appreciated it.
B.A.

Answer 1

Thank you for all responses. here is more info about the err message:
sy-subrc = 8
'invalid argument'
I looked up the invalid argument in note 99155 --> due to "The destination file is no longer available during repeated file access. "   So, the following steps were taken:
- file was regenerated and
- file was placed on the server to be read
have the following code:
OPEN DATASET FILENAME FOR OUTPUT IN TEXT MODE encoding default
                      MESSAGE D_MSG_TEXT.
also have tried the following:
   OPEN DATASET d1 for input in text mode encoding default.
   open dataset d1 for output in text mode encoding NON-UNICODE..
   open dataset d1 for output in text mode  encoding utf-8.
none had worked.  system --> status shows no unicode.
THanks again for any suggestions.