I have a ContentProvider class and is declared in AndroidMenifest.xml like this:
This sounds similar to an issue I had that was caused by an issue with the ClassLoader, see here: Bizarre behaviour when using Apache Commons lib in Android
This bug discusses an error relating to the class loader failing sometimes. The fix for me was to add this line:
Thread.currentThread().setContextClassLoader(this.getClassLoader());
in the constructor of the class that was calling the code that was failing.