It is recommended that an application should not attempt to open a file more than once during a response to an event, as it is possible that low level disk access routines within the operating system are unable to keep up. It has been found that when the filing system is stressed, performing multiple opens on the same file can lead to the ESL application locking for a period of several seconds. This problem applies to both FILEIO routines and native facilities to read and write data to and from controls.