First of all, thank you for reporting this issue. Unfortunately, both VIM 7.0 and 7.1 seems to be affected by this.
Main poller setting is correct - so if you see on main poller Recommendation engine Enabled, its really enabled.
Disabled setting on Additional website does not affect recommendations functionality.
If you want to confirm that recommendations are enabled, you can check log "c:\ProgramData\SolarWinds\Logs\Recommendations\Recommendations.Services.log" and there should be messages like:
- Recommendations recomputation was turned on. Groups with recommendations older than 24h will be recomputed.
- Recommendations recomputation was turned off
(log file is only on main poller machine)
Error occurs only when you click to enable recommendations engine, or anytime when you visit All Recommendations page on additional web servers?