I/O operation on closed file.

This error message typically indicates that a program attempted to perform an input/output (I/O) operation on a file that has already been closed.

In other words, the program may have opened a file to read or write data, but then closed the file before finishing all the necessary I/O operations. If the program then tries to read or write data to the closed file, it will trigger this error message.

To resolve this error, make sure that all I/O operations on a file are completed before the file is closed. Additionally, check that the file is indeed open before attempting to perform any I/O operations on it.