Internal error: invalid literal for int() with base 10: '' when opening main dashboard

Here the list with the error message
main dashboard
Internal error: invalid literal for int() with base 10: ‘’

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Linux Hosts
Problem while rendering dashboard element 4 of type combined_graph: Failed to calculate a graph recipe… Have a look at var/log/web.log for further information.
Windows Host
Problem while rendering dashboard element 4 of type combined_graph: Failed to calculate a graph recipe… Have a look at var/log/web.log for further information.

Ralf