It usually happens when you have custom work environment. In my case it was wrong Platform Builder install directory path.
If you use Visual Studio OS project to work with Win Ce go into Solution Explorer and open menu of OS Root field (typically named D:/WINCE/) and choose Open Build Window. Now you can write set to see all environmental variables. For more friendly browsing, you can also dumb set outcome to a file, by writing set > d:\wince_set.txt and then opening d:\wince_set.txt file in chosen text editor. If you will find any invalid path you can override it by choosing Project->Properties menu and then selecting Configuration Properties->Environment tab. Now you can correct invalid variable.