If you get this error than your installation of Miva Merchant Empresa v5.10 is missing a builtin configuration for the logging.so builtin. The file does not exist or there is no configuration variable for it in Empresa's configuration file.
Fatal error in mm5/5.00/admin.mvc @ [00000055:0000005a]: admin/log.mv: Line 27: Unresolved call to external function 'miva_openlog'
If Empresa is configured with a mivavm.conf the variable tag is:
builtindir=/path/to/builtins (the path will have to be changed to reflect server configuration)
If it's configured in apache's configuration file or an Include file than you are most likely just missing the builtin file (logging.so) as the variable tag for builtins calls on the entire builtin folder:
SetEnv MvCONFIG_DIR_BUILTIN /path/to/builtins
Follow this path and check this folder for the logging.so file. If it's not there you will have to download the latest version of Empres and put the file in the builtins folder.
Download the latest version of Empresa here.