Technical Blog Post
Status of IBM Installation Manager Product and Service Repositories
If you use default 'Update' in IBM Installation Manager or use the Web Install method to install the product, you are accessing the product and service repositories on IBM servers. (The main alternative is to download the zips of the product/fixpacks and host them locally.)
Occasionally, there would be issues and you would not be able to update/install. (There have been recent changes to improve overall reliability.)
There is now a doc which shows the current status of the product repositories on IBM servers.
Please check it if you are having issues updating or installing from the IBM servers.