Maria: Go to Control Panel>Data Sources and click on Open Data Directory. Then Look at Available Data Sources and select the appropriate data source. Then click on Open Data Directory. Then openM15 files using a spreadsheet like Excel or buy using notepad++. I selected these two options over just using notepad because they will count all the lines of data. Make sure all 200000 lines of data are there. If only 50,000 lines are there then that is the problem. If all 200,0000 lines of data is in the file then do the following: Go to Control Panel>Data Sources and click on Reload Data Files. See if this fixes the problem.
Notepad++ can be downloaded for free.