While performing URL Validattions for 3000 URL's using a REST Steo,  if there are 100 URLs that are all errored out (websites down or not authorized) the portal stops processing.  This looks like a limitation set somewhere within the portal.

In the portal, when you run test with  the 'RUN" option ,  it uses the pre-defined staging document of Run1user1cycle.stg.  This staging document has 'Maximum number of errors and failures before test is stopped set to 100. This is by design.  This value can be changed  by creating a custom staging document.  

All DevTest Environment

Create  a new staging document  or update the default Run1User1Cycle.stg  with Maximum number of errors  to a higher number.. 

In your  Staging document, look at the Report Tab,-> Default Report Generator "Maximum number of errors and failures before test is stopped:" is 100  which means, the Test will stop once it hits the 100 error count.
This value can be changed to a higher number depending on your testing scenario.
For example you could set it to a number like :  3000.

When running test in the Portal,  select the 'Run with Option' instead of 'Run' Option  and use the newly created /modified staging document.