ApplWindows is a control panel that provides the same type of functionality as the new WindowBOSS feature of PowerBar. Since both utilities modify System 7's Application menu, they are not compatible. This is the same problem you would have if you had installed one of the half-dozen or so hierarchical Apple menu extensions.
NOTE: Only the WindowBOSS feature of PowerBar is incompatible! You can still use the remaining features of PowerBar!!
You should turn off ApplWindows before installing PowerBar to avoid a conflict. Test WindowBOSS out and see if you like it. If not, you can turn it off while still being able to use the other parts of PowerBar, but be sure you turn it off before turning the other one on.
For PowerModule Developers
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PowerModule code resources and file types should now be of type 'Pmod' (they were 'PMod'). Note that the previous 'PMod' modules will still work, but any further development should use the new type.