I have started my first project using Hierarchial sheets. There are 6 sheets. The first few were ok, but now when I open the sheet, it complains it is unable to open some of the sheets.
I can access the individual sheets via Window Explorer and open them with Kicad 8, they open ok. But if I try to open the schematic via the root, I get the errors.
I think you need to upload a .zip file with your project before anybody can give you effective assistance. It does not hurt atleast 
Do the paths, shown in the error message, still correspond with your project? Have you moved files or folders around?
Bas
I was using the sheets for a few days before opening the project created these errors. The project was created under version 7, then saved to 8. I am currently using 8.02. Attached is a zip of the project files.
1047-metropolitan-line-position-indicator.zip (153.2 KB)
I have the same error here. I have no clue ofcourse as I am not a KiCad developer but I did think of a workaround.
I opened the lacking schematic files in a stand alone editor. I also opened the project. I than Copied and ‘special’ pasted the content into the empty hierarchial sheets manually.
There is only one sheet that is still empty.
Afterwards I could close and open the project normally. I added the zip file.
1047-metropolitan-line-position-indicator.zip (202.7 KB)
Good Luck 
Bas
The names don’t match. Using such long file names makes it difficult for humans to check.
The differences become clear when you copy & paste the names. Below “Err:” are the names in the error message, and “Zip:” is from the zip file names.
Err: met_line_east_Amersham_to_Harrow.kicad_sch
Zip: met_line_east_Amersham_to_North_Harrow.kicad_sch
Err: met_line_west_harrow_to_Amersham_sch.kicad_sch
Zip: met_line_harriw_to_Amersham_sch.kicad_sch
Err: met_line_harrow_to_Uxbridge_sch.kicad_sch
This is a psychological thing. Humans tend to not remember literal things, but give some meaning to things, and remember the meaning, while PC’s are simple minded compare literal characters in names.
Another thing to make your schematics easier to read (and your life easier) is to adhere to a flow of signals from left to right and voltages from top to bottom in your schematic. In some of your LED strings the signal goes from left to right, but in others from right to left. For KiCad it does not matter, but for humans this makes it more difficult to spot errors. Using the same direction also makes Copy & Paste easier.
ERC also spots some shorts in your schematic, for example:
Whenever you see a junction dot in an unexpected location in KiCad, it’s always a concern and a reason to focus on.
The file names refer to station names, so West Harrow is valid in this case, though there is a spelling mistake in harrow (harriw). So the mismatch is not as valid as it might seem here.
The flow of the drawing has nothing to do with signal flow and to the direction of stations. Hence the names that are on the schematic.
As to ERC errors, I had not got to that point in the project, so yes there may be connection errors.
What I am concerned about it why the errors opening the files from the project, while they open ok directly?
The sheet filenames in the project and saved to disc don’t match, not for the reason above, but because if you edit the filename in the sheet properties, it does not save the change to disc. I presume this is a possible bug in V8.02.
I can only assumed the files opened ok from the project until I edited the filename in the project.
I have renamed all the files, deleted the references in sheet 1 and recreated them again, with new file names.
I experimented with renaming the file, this time it asks if it wants to create a new file with the contents of the old.
So don’t know what was going on originally, but I have fixed it for now.
Multiple sheets seems clunky compared to EasyEda where it is a new tab sheet. But it is what it is, I don’t suppose it will change.
Hierarchial busses and labels are the bomb. My root sheets are like art work 
Off topic.
Are you going to make some kind of control panel for a model railway layout or something??
It is the first time I have used the hierachial sheets, I can imagined that some are like art work!
The design is to display the position of trains on my local tube railway. I have a program on a Pi parsing the open api from Transport for London and the circuit is for the display board using rgb leds and an esp32. The circuit is very early days and it is why it may not follow the normal flow of an electrical circuit, so it may yet change as I have not decided on the size of rgb led I am going to use. I do have prototype testing the software working fine.
That is one neat project.
I don’t know if you have room for it. But I know a guy who is making a control panel. He also uses modular blocks with not one but many PCBs. Besides d’em neopixels he also added those small I2C OLED displays so he can display the names of trains. 
Bas
