This error results from importing two modules with the same name. For example

import A.Util
import B.util

In this case, the default name given to the two imports is the same: Util. To give them different names, use the longer form of the import statement

import A.Util
import BU = B.Util;

Now a name N from A.Util can be referred to as Util.N and a name N from B.Util can be referred to as BU.N.