Ah yes, then we are indeed on a thick client. Apologies for being thick. :-)
Still no joy. Even after amending the Application Modeller wizard to set the application up as ""Mainframe (IBM)"", I still see the same outcome.
Using ""[pf16]"" in the value field within the Navigate item, if I choose Global Send Keys, it trys to type [pf16] onto the screen (resulting in the below message because there is nowhere on the first screen to type into).
Internal : Failed to perform step 1 in Navigate Stage 'F16 (not working)' on page 'Get PI Data from Mainframe' - Failed to send keystroke - Presentation space keyboard locked
If I use Global Send Key Events, BP will send something to the PCOM session, but PCOM doesn't accept the value being sent, eg: as if an unknown keystroke has been entered.
Update - Breaking News! I've managed to get it working!
After lots of trial and error, I finally managed to get it to send F16 to my terminal by using Global Send Keys with a value of ""@g"" (we already use ""@1"" for F1, etc.). I even set the Application model back to Mainframe (IBM PCom HLLAPI) as I didn't fancy a huge amount of regression of other existing processes, and it still works.
Still don't understand why previous attempts to use Global Send Key were physically typing the text onto the screen rather than 'sending', but it works for now, and that is good enough for me in the short term!
Thanks for your help Chris. Certainly gave me some other options worth trying.