Basic guide to using the -show_err function in RTW and BI
-show_err is the basic error reporting system for RTW and BI (it is not available in M2TW), to activate it do the following:
Right click on the desktop shortcut you use to launch your game. Select properties. In the target line after the end " type a space and then -show_err
the finished line should look like: click apply and that should be done.
Please note that -show_err only gives message for the first problem it finds. You have to fix the first problem before you get next message. For some problems you also need to delete the map.rwm file in order for first problem to be removed. If you have a non-fatal error that gives message, you do need to fix it, otherwise you won't get message for more serious problems.
If you have a KTM (return to previous menu) problem you will not get the -show_err message until you completely exit the game.
 Understanding messages given by -show_err
Once you have -show_err operating you will find that for some modding problems it very kindly gives you a reference to which file is wrong and gives you the line number where problem is located. (to find line number x use notepad, edit, go to function) Unfortunately a lot of the error messages it gives you are more difficult to understand. Some of the common confusing ones are listed below:
"Expected faction - must add at least two factions to the world" apart from the obvious that you haven't added two factions, this KTM message normally means you have an error in descr_strat (message should also have given you line number) the error will normally be one of formatting or spelling which serves to stop game reading file before the point that it gets to 2nd faction. Trying to use a 1.2 file in 1.5 patch does this as the win conditions section is not recognised. Comments in the resource section that have lost their ; also do it, there are many other possible ways of getting the error.
"The child character xxx has no father and will be omitted from the game" Means you have too many children for one father you can only have 4. Any more don't appear and generate that message when you quit game.
"Script error at... could not find next child. Children list must be terminated with an end" this doesn't often literally mean you don't have ', end' on the relative line. It more often is that line has some other problem, for instance including a child that doesn't either have army on map or a character record line.
"Script error in .../descr_strat.txt, at line xxx, column x. You have chosen an invalid tile(0,0)for the settlement of" Where line xxx is the bottom of the descr_strat file and the settlement name is not specified. Caused by pixels on map_regions.tga of a colour that do not belong to any region colour specified in descr_regions.txt - watch out for merged colours when editing map_regions.tga as that is usual cause.
"Script error in .../descr_strat.txt, at line xxx, column x. You are trying to place zzzz in this region(yyyy), but it already has a settlement(zzzz)."- can be caused by using an almost black pixel for the effected cities location on the map_regions.tga - the pixel must be RGB 0,0,0
This error can also be caused by listing a region twice in descr_strat.txt
"Script error in ..../descr_strat.txt , at line xxx. You have chosen an invalid tile (0,0) for the settlement of" If settlement is not named and the line xxx it gives you is the bottom of descr_strat file, that normally means you have a spare colour in map_regions.tga that does not belong to any region defined in descr_regions.txt (that problem can also cause straight CTD and I'm not quite sure what causes difference)
If settlement is named and line xxx is it's listing in descr_strat.txt, then problem is because settlement is placed on invalid terrain. This may include being over river location, over impassable forest, or mountain ground types, or being over area marked as sea in map_heights.tga. The last includes areas of 'land' which are true black RGB 0,0,0 as the game takes them as sea unless a map_heights.hgt is created.
"Cant find texture blah_blah.psd" Message with CTD on attempting to load battle map, assuming your descr_model_battle.txt doesn't actually ask for blah_blah.psd, normally means you haven't put texture line in DMB for faction that's attempting to use unit, so show_err is referring to the default texture for the model (you shouldn't actually need to alter that - just make sure unit has a correct texture line). Watch out for officers, crews and mounts with this one as well as basic soldier.
 Problems that crash or KTM without -show_err message
Some examples of common modding problems that don't generate show_err message are listed below, to help narrow down possibilities.
- Too much sea area on new map = CTD before generation of new map.rwm
- Problem with rivers in map_features.tga, 2 pixel square block of 'river' or river without ford that divides region = CTD before generation of new map.rwm
- Using misspelt name in descr_strat or one that doesn't belong to the correct faction (look up descr_names.txt to check) = CTD on loading campaign
Would everyone else please add more explanations / message less CTD's as they come across them. Thank you