If you have to redownload Dolphin everytime it fails, then something may be changing the original exe (virus?). This is not a normal behavior for any program, I don't think Dolphin is the cuase. Also try to run it as administrator if you are sure you are virus free.
Rig
*Corei5 3570K *Nvidia 9800GT 1GB DDR3
*Motherboard Asus P8H77M-PRO *Win7 x64
*RAM 8GB DDR3(1600)