If ESL is unable to load the external string DLL when starting a program, an error message is displayed and the program is aborted. An error message is also printed in the error log, see EsIXstrSetPrimarydll for a list of the error codes.

If ESL is unable to find a particular external string in the DLL, an error is written to the errorlog. The string "XS# 123." will be used in the program, where the number will be the identifier of the missing string. When text like that is displayed, it means that an incorrect or incomplete resource DLL is being used.