Recently, I contacted all of the Skimmer operators who had recently contributed to the RBN and were running anything other than the most recent versions of CW Skimmer or Skimmer Server. The reason for doing this was to encourage them to update because 1) it's free and 2) there was a bug in earlier versions that caused some of the "False CQ" spots that have plagued us.
On the theory that "no good deed goes unpunished," it turns out that updating to the most recent versions of CW Skimmer and Skimmer Server may undo all the good efforts people made to correct their receivers' calibration, if you are using Windows 7. The reason for this is that the .ini file in which the frequency calibration data is stored, which used to be located in the program directory, was moved in the most recent versions to an "application data" directory. What this means is that if you added a line for Frequency Calibration to your .ini file in the program directory, that correction may have been lost when you updated. If you are using Windows XP, nothing has changed, and you don't have to do anything.
For Windows 7, here's the solution, or rather two approaches to it. First, you need to identify where your new CWSkimmer.ini or SkimSrv.ini file is located. One way is to start CWSkimmer, open the Help menu, and select Data Folder. This opens Windows Explorer and the folder where the CW Skimmer.ini file is located. Click on the up arrow in the top of Windows Explorer, to go up one level in the path, and you will see folders for both CWSkimmer and SkimSrv. The .ini files are located in these two folders, which are sub-folders under Application Data..
The other way is to use Windows' Search feature to find the .ini file you are interested in. If you go this route, just search for either CWSkimmer.ini or SkimSrv.ini. Be sure to set your Search options so that the search will include system and hidden files. You will find two - one in the program folder and the other in an Application Data sub-folder - the one in the program folder is your old one, and the one in the Application Data sub-folder is the one that is currently active.
Typically, Windows 7 users have reported that the .ini file winds up in C:\Users\[username]\AppData\Roaming\Afreet\Products\CwSkimmer or C:\Users\[username]\AppData\Roaming\Afreet\Products\SkimSrv.
Now, the fix. You can either copy the relevant .ini file from the program folder to the Application Data sub-folder, replacing the one that the new installation put there. That will transfer all your settings, including your Frequency Calibration line. Or you can simply copy that line into the new .ini file. Restart Skimmer or SkimSrv and you should be back on frequency.