Connect to SAP Gateway failed: Since this morning our users have been getting an error message and cannot work with GuiXT. The error message is a popup with title "RFC WWW_DISPATCH_REQUEST" and the text says "Connect to SAP Gateway failed". The error doesn't occur if the users work with a SAP Logon to an application server instead of using the message server. How can we rectify this?

This a networking issue, related to firewall settings or IP address translation.

From the message server, the SAP Gateway on computer 10.40.yy.yyy cannot be reached via port 3300.

Is a

ping 10.40.yy.yyy

on the message server ok? Is port 3300 open in the firewall settings?

Since "ping" cannot check an indiviual port, you can use "psping" from

psping 10.40.yy.yyy:3300

I hope that you can narrow down the problem with these tools. Also, it helps if you can find out which network parameter has recently been changed. In Google there are a couple of additional hints; search for  "connect to sap gateway failed".