Enterprise Library Pitfall

I was recently asked to bugfix an application. The bug was eaasy enough to fix, just add two lines of code, no big deal. In order to build the application I had to install Enterprise Library 3.1 and re-reference a few .dll files in it. Also no big deal, done it before with previous versions of Enterprise Library... but it turns out i stumbled right into a configuration pitfall!

Short version for those who dont want to read Tom Hollander's blog about Avoiding configuration pitfalls with incompatible copies of Enterprise Library:
If you install Enterprise Library 3.x a go with all default options/choices, you end up with two sets of .dll files. If you have to re-reference these files in a project and use the wrong .dll your code will compile but throws an exception in runtime... referencing the other set of dll files will solve the problem (but might cause new problems as well).