When running the Go To Meeting test session from here I got an error code of 1392. When opening the log below I saw the following:

08:43:56 2CC8 I: created file ‘C:\Users\username\AppData\Local\Temp\26\B0560F7D-757E-4C65-A168-2364C6F4606F\G2MCoreInstExtractor.exe’

08:43:56 2CC8 E: Installer launch failed; command was: “C:\Users\username\AppData\Local\Temp\26\B0560F7D-757E-4C65-A168-2364C6F4606F\G2MCoreInstExtractor.exe” “/Action Join” “/EGWAddress 216.115.208.230” “/EGWDNS egwglobal.gotomeeting.com” “/EGWPort 80,443,8200” “/MeetingID 333699349” “/Mode Terse” “/Product g2m” “/colClientUiReadyEvent Global\BC84F869-6926-4A19-9926-7111917D85E8” “/sessionTrackingId ul-0396-0714-9b0e-beb9799efb97”
08:43:56 2CC8 E: [installEndpoint] completed: 2001 (ECError::eSomeError), Method “CreateProcess” returned Win32 error [1392]. The file or directory is corrupted and unreadable.

From what I could see, the launcher had two stages. The first was to download
G2MCoreInstExtractor.exe.

08:43:56     2CC8 I: created file 'C:\Users\username\AppData\Local\Temp\26\B0560F7D-757E-4C65-A168-2364C6F4606F\G2MCoreInstExtractor.exe'

The second would launch that to download the remaining files. This is where it appeared to be failing.

 Installer launch failed; command was: "C:\Users\username\AppData\Local\Temp\26\B0560F7D-757E-4C65-A168-2364C6F4606F\G2MCoreInstExtractor.exe" 

The issue was not that it was failing to launch but that it was failing to download in the first place. The proxy server had an ‘allow .EXE file downloads’ set for GoToMeeting.com but not for the GetGo Content Distribution Network which hosts the file G2MCoreInstExtractor.exe. Adding the GetGo URLs that host the GoToMeeting file to the allow list resolved this:

getgo.com:443/builds/g2m/
getgocdn.com:443/builds/g2m/
getgo.com/builds/g2m/
getgocdn.com/builds/g2m/