This message is typically due to the allotted memory setup for PHP being exhausted. Check this site for an explanation of what to do. There are a few places that values can be changed.
This can also sometimes be due to the size of the plugin being uploaded. Intense is rather large, so you could look into this link as well.
Typically, when these issues come up, we suggest to manually install Intense (via FTP) the first time. It takes a little more work, but it should guarantee that you won’t have upload issues. If there are memory issues, you’ll have those show up once the plugin is installed as well, so that one is worth looking into.