following MWE gives a strange error "(interwoven alignment preambles are not allowed)" when processed with lmtx:

\definetabletemplate[fosa][s0|xp(3.5cm)|lw(0.7cm)|xp(5cm)s2|lw(2.5cm)|]
\starttext
\starttable[fosa]
\NC Cell 1 \NC\Use3[p(8cm)]{A longer cell}\NC\AR
\MR
\NC Cell 1 \NC Cell 2 \NC Cell 3 \NC Cell 4 \NC\AR
\stoptable
\stoptext

No problems in mkiv.

I think Use3 is the problem, but I'm not sure...

Many thanks for your help

Christian