Ah sorry, I should've said that I'm editing in V5.80 and creating an operation from scratch rather than editing.
The steps I've taken are the ones in the operation editor manual, sorry to cut and paste:-
1) make an operation project, set operation settings in config file 'src\<project
name>.ods' using Calc application from LibreOffice software;
2) create description for platoons and reserves in config file 'src\<project
name>_div_pool.ods';
3) write text-description for operation and do all necessary localizations in
'src\< project name>_text.ods';
4) add picture '<project name>_op_image.tga' that will be placed next to
operation name in the game list of operations. The picture must be 160x100
pixels, TGA 32 bit.
5) convert all files into binary data using Operation Editor;
6) draw briefings in 'briefs\op_brief.odg' using LibreOffice Draw;
7) convert briefing graphic by pressing [Ctrl+G] in the editor;

write briefing script '<project name>_scripts.engcfg' (text file in ANSI code),
specifying scale, adding graphic description from steps 6-7. Convert the
script by pressing [Ctrl+H];
9) using Operation Editor place platoons, set controlled territory, weather
conditions, key points, terrain settings, define tasks and objects for AI;
10) when all settings are set, compile the operation project and, if no
errors will be detected, new operation will be automatically added to the list
of available operations in the game menu.
All appears to be okay in the editor at step 9, I can see the units I defined in div_pool and the operation compiles without any errors... but then the operation isn't shown in the campaigns list. I'll try and host the files somewhere if I can.
Using the V5.80 Operation Editor I can create a template operation that I can run through the steps above and see in the game... it's very perplexing! In some ways I wish it were in text files rather than open office.