On the back of the synth there's a "Memory Protection" switch - flip it over and you might get lucky.
BTW, in the manual page 4, the description looks like it may be the opposite of the logical assumption, that when the protection[i/] is off, you can write patches - I don't know which way around it actually is:
"11. Memory Protection On/Off - When off, prevents the MatrixBrute's patch Preset and sequencer Pattern memories from being overwritten."