Error loading schematic - invalid symbol library definition in input/source

[JCollins]

I am trying to load a schematic made last year in KiCAD 5, in KiCAD 5 still, however am encountering an error on opening:

Error loading schematic file "...".
invalid symbol library definition in input/source
"..."
line 1411, offset 2

Inspecting the file, line 1411, offset 2, is a line calling a fuse device:

EESchema Schematic File Version 5
...
$Comp
L Device:Fuse         <-- Line 1411
U 1 1 63417752
P 5150 6200
AR Path="/63417752" Ref=""  Part="1" 
AR Path="/63417752" Ref="F1"  Part="1" 
F 0 "F1" V 5347 6200 50  0000 C CNN
F 1 "F100m" V 5256 6200 50  0000 C CNN
F 2 "" V 5080 6200 50  0001 C CNN
F 3 "~" H 5150 6200 50  0001 C CNN
	1    5150 6200
	0    -1   -1   0   
$EndComp
...
$EndSCHEMATC

Making some crude file edits, I can see that if I comment a component (add leading ‘/’ symbols to component lines), the next component turns up with the same error on the equivalent line. Completely removing all components prior to $EndSCHEMATC, and the file opens albeit with many missing components.

I can’t imagine a Device:Fuse being problematic, and it almost feels like there is a component limit issue…

Any ideas?

NB: The misspelling in $EndSCHEMATC does not appear to be a typo on my part.

Further Information:
It appears that anything that isn’t a ground node, power node or label node does not want to show up. When deleting components and successfully opening the file, these are the only objects left. When I edit the file and add a Device:Fuse, the addition is successful.

Further Information 2:
The issue seems to come from two areas:

1. The symbol name not being saved to the $Comp$ definition and
2. the same definition having two lines:

AR Path="/634188CD" Ref=""  Part="1" 
AR Path="/634188CD" Ref="F2"  Part="1" 

Adding a component name and removing the AR Path directive makes the file openable.

$Comp
L Device:Fuse F2 / Added 'F2' name
... / Eliminate `AR Path` lines
$EndComp

If I have to manually repair the file this will take some time. Is there any good reason why these errors have occurred and how can I avoid them in future?

[der.ule]

Not sure what is going on, as I haven’t had such a case while using KiCAD, but to help other people try to figure it out you should add the complete version information of the KiCAD that originate the file (if still possible) with “Help->About->Copy Version Info” and the complete version that you are using to try to open the file.

Some other useful information to know would be if the you are using network shares, if several people access the same files at the same time, if you are using some kind of version control, etc. Basically a bit more about your setup and circumstances.

An last, you could try and use the latest KiCAD version and see if it can import the files by itself (both V5 and V6) can be installed along each other.

I hope this helps.