Request Error on NETXMS data source

I use the NETXMS data source and all works fine, but I have 50 remote sites to plot metrics, I added several queries (29 - A to Z plus 4), but when I try to add one more the graph stop to show results and icon “!” appear on the left upper side with message Request error. If I delete the query, the graph works again.

The most strange is when using the “Explorer” option, the graph appear without errors.

Is there a problem with Grafana ou NETXMS data source?

The Grafana version is v6.0.0-beta3 (commit: 19192fc)

Thank’s in advance!