I tested the same on more that 20 sites and all worked fine.

There is nothing from your error that shows about a DSLocalizator problem. I need more information:

1) Your DNN version, you said 5.4.1 and your error says 4.5.3 (As the last version is 4.5.3, I will suppose that it is your installed version)

2) What other modules/engines are installed on your site (Specially pageblaster, Blowery, Ventrian's URL re-writer, Inventua's URL rewriter, etc)

I need all the information at your side for me to try to reproduce here (More than 5000 users using DSLocalizator right now without that problem)

B.T.W. I am not saying that it is not a problem with DSLocalizator. We must try to determiner the COMBINED rules to allow the problem to reproduce and then fix it.

Note: Allowing me to access your site could help also.