Alan5758 is correct that an antivirus program running in the background can cause serious problems.
However, in fairness to Prolific/Jim/etc., it should be noted that the installation wizard specifies turning off anti-virus programs as follows:
"SereneScreen Aquarium asks that you disable any Virus scanning software before continuing installation.
"This is not required, but it may ensure a proper and complete installation.
"SereneScreen Aquarium requires DirectX 6.0 or greater in order to function properly. If you do not have DirectX 6.0, you should download and install DirectX from
http://www.microsoft.com/directX/."