With this error message the FRITZ!Box informs you that the data rate of your DSL connection is lower than it could be, and this problem results from your current DSL cabling.

For the entire data rate of your DSL line to be available, the FRITZ!Box must be connected directly with your household DSL connection and from there directly to the responsible exchange.

To resolve this problem, make sure that your DSL line does not include any branching or multi-distributors. For instance, you may have telephone jacks branching off from the DSL line. If you have multiple telephone jacks in your home or apartment, connect the FRITZ!Box to another jack and check the "System / Event Log" menu in the user interface to see whether impairments of the DSL signal are still detected.