Entering the CLI command installed-systems add <URL> generates an error and terminates the current SSH session to Management Center:
"
terminate called after throwing and instance of 'std;:runtime_error'
what (): Negative integer can not be converted to unsigned integer
"
These errors were reported on Management Center version 1.5.x and 1.4.x and prevent upgrading Management Center to a higher software version.
Rebooting Management Center does not help.
It was unknown how the Management Center goes into this state.
This issue was fixed in Management Center 1.6.1.1.