The isolation method is a simplistic approach to pinpointing general errors.
It is often used when no information is given in an error such as the "cluster protal saw into cluster" error. Despite relating to a very specific point in the map no information is given as to where that point is. Isolation is a standard approach to finding this type of error.
The method is simple and systematic. It uses the Cordon Tool to compile only part of the map at a time.
Start by isolating half the map with the cordon tool and recompiling. If at least one of the errors being tracked was found you half that area. If no errors being tracked were found you move over to the other half of the area. The approach is then repeated in the same manner until at least 1 error has been pinpointed.
Fixing the error
After you've found the error it often becomes the problem of finding out whats wrong within that area. The simplest approach is to back up your map at this point. Then delete the area object by object recompiling each time. As soon as an error goes away return to your backup and try deleting the last deleted object and recompiling. If the error goes away you've found the cause. Leaving the object deleted or trying to find the problem is entirley situational and up to the mapper. But you now know the cause and can stop the error.
With generic errors this is often the best approach to take. Depending upon your computer and map multiple recompiles may be time consuming but it will only get faster each time. Plus the ability to fix errors yourself and not wait for two days on a forum is always a benefit. The isolation method is one any mapper should be familiar with.