Please do the following,
 
While IncrediMail is running you can always see the IncrediMail Tray Icon (orange envelope) that is located in the lower right corner (near the computer clock).
 
Right click on this icon and select: "Exit".
 
1. Go to C:\Program Files\IncrediMail\bin\Licenses. 
 
Delete the "IM_PREM.imk" and "IM_LTWIZ.imk" files.
 
Note: Delete only these two files and not any other file.
 
2. Go to C:\WINDOWS. Delete the files MF_C420.lfa and MF_C421.lfa .
 
3. Go to Start->Run, write the word: regedit. 
Go to: HKEY_LOCAL_MACHINE\SOFTWARE\IncrediMail\DefaultAnimations
 
You should arrive at the "Default Animations" folder. Within that folder delete the MF_C420 and MF_C421 files.
 
4. Open the IncrediMail program and insert the codes again.
 
Note: If you have Windows NT or 2000 you should look for the files in C:\WINNT. 
 
Do not delete any other key or file other than the ones we directed you to.
 
Open IncrediMail and register your registration code again.