Hi,
sore for late response. Unfortunatelly, license server doesn't provide demo licences, so in this case clients need to be activated manually. This can be done in two ways:
First possible solution is documented
here under section "Activating demo licenses on render nodes" (the article is written for 3ds Max, but solution for C4D should be the same except request key will be stored in "request-c4d-commercial.txt").
Second possibility would be starting full C4D on client at least once so demo is properly activated. This is probably not the best solution in lot of cases (since you might not have full C4D license on client machines). We plan to improve this by allowing users to activate demo from TR client directly - hopefully this should be included in next daily build.