This is probably best explained with an example. I have the following table, where the \"A\" cell spans two rows, and the \"B\" cell spans two columns.
I came across a similar problem, but had to use \multirow{specified width}{} instead of \multirow{*}{}. Nesting multirow inside a multicolumn does not work in this case.
I found \multirow{specified width}{\centering text} to work instead.