IW 15.5.10 Sendfile

[Mikael Nilsson]

>>    WebApplication.SendFile(UserSession.ViewThisFile, False, '', ExtractFileName(UserSession.ViewThisFile));

It's possible you need to add the mime type in the 3rd parameter instead of the empty string.

What is a mime type.
And remember SendFile has worked before IW 15.5.10