Programming Question: Open Cursor failed ,why ?

Hello I hope you can help me. My Problem is that in my programm an open Cursor statement failed, sometimes. The error number 243 says : The database server cannot set the file position to a particular row within the file that represents a table. And the isam error 111 says: The ISAM processor cannot locate the requested record. For C-ISAM programs, no record was found with the requested index value or record number, depending on the retrieval mode in use. Could it be that if one try to open a cursor (after prepare and declare) for a select, that no records found, it ends in with a failure ? My is theory is that if someone delete all records between the commands prepare, declare and open the open cursor statement failed. Can you say if this theory is correct ? And can you say me how a open cursor react if i delete some records concurrently. Thanks for any answer Thorsten