Hello,
You may need to manually remove the game folder, and delete 2 Registry Keys then try a re-install.
Go to C:\Program Files\Stardock Games\Sins of a Solar Empire (or where ever you installed the game) and delete the main folder.
Then launch the System Registry (Start-> run, and type regedit)
Look for and delete the following Keys;
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sins
HKEY_LOCAL_MACHINE\SOFTWARE\Stardock\Drengin.net\sinsentrench
For Vista 64 bit;
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sins
HKLM>SOFTWARE>Wow6432Node>Stardock>Drengin.net>sinsentrench
Then, reboot your PC and go back to Impulse and try installing the base game. Make sure it installs to 1.13 version, test it out before then installing entrenchment.