Problem: When using the dcolumn package to decimal align a column in tabular, if you try to put an equation in the first row of that column as a header, LyX generates an error.
I searched the archives and Herbert's page for this issue but could not find a solution. After much trial and error, here is the solution I found: dcolumn automatically puts everything in math mode, so by putting in a LyX equation it generates another begin math command or $ which causes the error. Workaround 1: Use ERT to enter your equation but leave off the $, e.g. ERT:x_5, instead of $x_5$. Workaround 2: Use multicolumn in Layout...Tabular. Just select the single cell. Then you can enter a LyX equation with Ctrl-M. The second option produces better results since it will center the equation in the cell. The first option will try to align with a decimal in the equation..if you don't have one it will align the end of the equation with the decimal. Steve Buonopane