If there is a syntax error within your data file, the compilation process (Log | Create a Log or Compile All Logs options) will halt, the program will display a message box, and it will display the tab in which the error has occurred. The exact contents of the message box will vary depending on the type of error.
Check the required format for the datasheet(s). (See LogPlot Datasheet Summary.)
When you have made the necessary corrections, try compiling again.
! Note that you do not need to save the data file prior to recompiling - LogPlot will read the data directly from the Editor window. Don't forget to save the changes you make, however, prior to quitting the program or closing the data file!