Found a fix for E-file error: 504 ( Gateway Timeout) Individual Filings

Assuming that your internet connection is good and that you are able to file other clients:

Remove all pdf attachments.

Clear the e-file under E-file/e-file support tools/clear return/return

Go into the Lacerte/21tax/IDATA/EF

Locate the client file NAME.IE1

Rename the file NAMEold.IE1