For people using window vista

Step 1: Go to your Maplestory client main folder.
(Default is set at C:\Programs Files\Nexon\Maplestory\).

Step 2: Select "Properties".

Step 3: Click on the "Compatibility" tab and check "Run this program as an administrator"

Step 4: Click on "Apply" and select "Ok".

Now you will be able to run SolitaryMS without any issue