Modpack version
1.74

Issue
When connecting OpenComputers computer (using it's adapter) to ActuallyAdditions Item Interface (with Item Laser attached, but I haven't tested without it, should probably crash too) and calling any method except getDocs, the game will crash. After loading world again computer displays error "Unsupported method". This is similar to MightyPirates/OpenComputers#2996 but this time causes game to crash. My suggestion is to disable CC-oriented peripherals support in OC to prevent them appearing as available components but looks like there is no config option for it.

Logs
Two of them, second one created with VanillaFix installed
log1
log2

Thanks for the report, I'll have a look at what we can do.
Actually, I have no freaking idea. I'm not sure we can even remotely help here :P
If you have any ideas, I'm all ears.

Tested it again, this happens basically with every tile-entity with inventory attached to OC adapter. It is possible to disable some of Plethora functionality (as described here), but this is not a good solution since this will disable such functionality for ComputerCraft as well.

Dammit. I suppose the best solution would be to keep this bug open for people coming across the issue.

Fixed in Plethora 1.2.3!