This approach numbers all tables correctly in LyX and LaTeX. It has the drawback that a table in a "floatrow" environment is not listed under "List of Tables" in the "Outline" side bar of LyX.
In Local Layout under "Document settings" add the following code and "validate" it.
Style FloatRowTableCaption
LatexType command
LatexName caption
OptionalArgs 1
LeftMargin MMN
LabelSep xx
Align Center
LabelType Counter
LabelCounter table
LabelString "Table \arabic{table} (FloatRow):"
End
Add to the LaTeX Preamble:
\usepackage{floatrow}
In the LyX document create a Figure-float
- put
\CenterFloatBoxes\begin{floatrow}\ffigbox{ as ERT/TeX code at the beginning
- insert your image...
- put
}{ as ERT
- after the Figure caption put
}\killfloatstyle\ttabbox{ as ERT
- insert your table...
- put
}{ as ERT
- as new line insert the table caption and choose style "FloatRowTableCaption"
- put
}\end{floatrow} as ERT
Here is a picture how it might look:

floatrowpackage you must not loadfloatorrotfloatto usefloatrow. – May 29 '13 at 15:27