Nimbuzz is not compatible with the Nokia C5-00, you can check this here. You can delete the application off your phone via Menu > Applications > Select Nimbuzz > Options > Delete.
There are similair applications available in the Nokia Store.
Hope this helps.
You're right, I've checked the wrong version of Nimbuzz.
The application has most likely not been installed properly. First, delete the application off your phone like I advised in my previous post.
Once the application has been deleted, update or reinstall the current software of your phone with Nokia Suite. You can find the available updates, or reinstall the current version, when you click on the green arrow. Now reinstall the application by going to the Nokia Store > My Stuff.
Please let me know if the application still doesn't work so that I can research the issue further.
Apologies for the confusion!
Let me know how you get on.