Google Analytics has a limit of 9 dimensions in a report. You can still choose more than 9 fields in a report, providing some of those fields are metrics. Each report can include no more than 9 dimensions (for example Date, Source, Medium, Landing page etc), but can include any number of metrics (for example Sessions, New visits).

The limit of 9 dimensions applies also to any dimensions being filtered. For example if your report included just 9 dimension, but you added a filter on a 10th dimension, then that would exceed the limit of 9 dimensions, because SyncWith would attempt to run your report with 10 dimensions so that filtering can be applied.