If this is an ecoinvent unit process system, then it can be really large even if your own processes are not many. To fix this, you first need to find out the reason for the error. The error is logged in the log file. You can search there for "caused by"; check also in statistics how many processes your product system has. You can also unselect some of the options for the export, with everything checked the excel file is 500 MB or so. Success!