Hi Mukhtar,
Unfortunately it sounds like your log files have been moved or deleted. SignalExpress is still looking for the log files as your project (.seproj) includes references to your log files. The project you have saved does not have any measurement data in it, so the files cannot be restored from SignalExpress.
To find where the files should be, you can go Tools >> Options and select "Logging" on the left; this will show you where log files are stored. It will also tell you where the log files should be when you open your project (in the message window you mentioned).
It might be worth searching your computer for the files (copy their names from the message you get when you open your project) in case they have been moved. You could also check your recycle bin in case they have been deleted. If you find the files, move them back to the correct log directory. If you cannot find the files, it is likely they have been permanently deleted and cannot be restored - you must run your measurements again.
Hope this helps,
Tom
Applications Engineering, NI UK