SeaBlock/data-updates.lua:643: attempt to index '?' (a nil value)
stack traceback:
SeaBlock/data-updates.lua.643: in main chunk

Seablock (0.4.4)
factorio .18.24

Only installed mods required for this, is the only one that has an issue thus far

Just installed the mod and I'm getting same error message

Me too. Cannot play Sea Block (tried multiple versions of base game)

SOLVED by looking in one other thread here. Adding "Bob's Metals, Chemicals, and Intermediates" resolved my issue.

And now I am up on base version 0.18.30 and it seems to work alright.

Thank you, republikanen.
That fixed it for me.
My error was the same as OP but on line 696.
Now using
base 0.18.30
Sea Block 0.4.5

Gross I dont want bob's junk... perhaps add an actual fix