There are a few possible reasons that can cause this error.

The first solution to attempt:

• Make sure you have the key file (for versions 2.4.0.1- .2.4.0.3 the file is called "backup copy"), and remember the access code (in versions 2.4.0.1- .2.4.0.3 it is called "password for the backup copy")
  
  
• Start WM Keeper in "initialization mode". This option allows you to logon and bypass the earlier paths to the files. The option is available in version 3.0.0.0 and higher. Go to the Start menu > Programs > WebMoney > Run "WebMoney Keeper Classic 3.0.0.0 in initialization mode"

If the error persists:

Make sure you enter the correct password. You can do this with the help of the support service. For more information about password verification, read here.

Attention!

Due to a number of technical reasons the system responds to the wrong password in a number of different ways. Although it is not possible to login with the wrong password, the error messages can be different. "Serious error" is just one of them.

When you receive your correct password, run the program in initialization mode as described above.

If the above was not helpful:

You may be using an expired key file. WM Keeper has a "change keys" function. If you try to use the old file, you will get the error message. Contact the support service and they will help you find the right file.

Also see:
What is a key file