With such messages, you have the classic Stromer ST1 (there is also the ST1x, which is very different, as wll as the new ST1).
Unfortunately, no real solution can be given. These errors are erratic, but luckily not serious (mostly). Often, a restart is sufficient, sometimes the temporarily removing of the battery helps. Even the hard way, switching the system off and on again while riding can help (but keep the feet off the pedals while switching on).