I know nothing about GoDaddy but I can already tell you the first thing you need to do is follow the error message.  You need to change the error mode in the web.config file so you can see the actual error.  The current screen in the post does nothing to help you solve the problem, and only indicates that you have an error.  Once you alter the web.config you will see the actual error and can go from there.  If you don't recognize the problem after that, please post the problem and we can see if we can help. 

As an addition, I have decided to try GoDaddy for hosting and have ran into the same issue.  It does seem to be a problem with the html module but it probably is not.  GoDaddy has serious issues with the way they configure their hosting.  The problem you are running into is that creating the child portal somehow created a sub-folder underneath the install that should not exist.  If I had to guess the subfolder titles supplierportal.  The install is looking into the supplierportal folder for the DotNetNuke install where none actually exists.  My current fix, although not ideal is to do this.  In the supplierportal folder create a file called index.html.  In index.html place javascript to redirect to the correct portal alias.  The way this works for me is I redirect to the a url that looks something like the following,http://parentportalurl/Default.aspx?alias=childportalurl.  Like I said this isn't the best but it does work.  GoDaddy is doing something stupid with the way they configure their hosting.  So far their technical support is completely unknowledgeable and unwilling to even answer questions honestly.  Overall I am not impressed with them, and considering they are offering installs of DotNetNuke,  they really don't know anything about the product.  I may not be able to afford to move off of GoDaddy so my only alternative will be to move my install back to the server I have been running for a couple of years now, but if I were you I would find a different hosting company.  I have tried to work with GoDaddy on figuring out what the problem is but they won't answer basic questions and most of the conversations come down to me saying please answer my question and them replying we can't meet your needs.  I am mildly shocked but their customer service is terrible, the worst I have ever seen, and they seem to not have a clue as to what they are actually doing.  What is makes this even worse is I figured this out within 1 week of using them as a host.  I have barely had time to setup my old install and I already can tell they have serious issues.