Hi.
If you can share with us more on where you see this error, how consistent it is, what specific query or use-case you're running it'll help.
Generally, what this error means is that it's having trouble getting information from the Artifact endpoint. The Artifact endpoint is a upper-parent (an ancestry) class of all artifacts. When querying this endpoint then you're basically asking for all artifacts that match your filter.
I imagine that Work Views may be such a place where you are allowed to select different types to be included, but again, if you can share your use-case it'll help.
Also, please take a look at this thread:
c# - Can't query/order on built-in rally fields "could not read all instances of class com.f4tech.slm.domain.Artifact" -…
This essentially says that you can't (or shouldn't) just query this endpoint without specifying the exact types of artifacts you are asking for. It may be that it'll help us here.
So, if you can share more - we'll appreciate it.
Thanks,
Sagi