There seems to be a problem introduced in the 2007/12/10 beta related to tables with rowspans.  The following doesn't compile:

\starttext
\setupTABLE[split=repeat]
\bTABLE
\bTABLEbody
\bTR
\bTC A \eTC
\bTC B \eTC
\eTR
\bTR
\bTC[nc=2]
blah
\eTC
\eTR
\eTABLEbody
\eTABLE
\stoptext