I tried to find all *.rul files containing the text 'Some Text' but I was too fast entering the data. As a consequence I put 'Some Text ' in the Look for field and 'C:\Temp\*.rul' in the Look in field (see screenshot). This is not how you are supposed to use these fields but if you press Start with those values entered, MC crashes. Oddly enough, when I try with *.txt or *.sql it doesn't crash.
Since I can reproduce this error a crash dump is available if needed.
Version: Multi Commander v3.1 (build 1385) 64 bit Edition on Windows 7 Professional x64 SP1.