The serial numbers must be input exactly as shown, including the hyphens.
There are no capital letter O's in the serial numbers for Carrara, Bryce, Mimic, or DAZ Studio. These are the number zero.
If you copy and paste the serial number into the field, make sure there are no extra characters. This happens often, especially with extra characters after the sequence. The extra values will be invisible and the only way to check this is to put your cursor in the field and arrow ahead. If it doesn't stop immediately after the last character, then there is extra spaces that you should delete.
Make sure there isn't any security software running during the install or the activation process.
Make sure you are logged into the account with administrative rights--in other words, the account that can install software. In Windows Vista, you may need to right-click on the actual executable and left-click on 'Run as ...," then choose 'Admin.' For example, for Carrara, you should find the Carrara.exe file and then right-click on it and left-click on 'Run as ..." Then choose 'Admin.' You may need to enter the serial number for this use (session) of the application, but the next time you launch it, you shouldn't need to re-enter the serial number.