The AbstractNodeData.getReferencedContent() at some point calls hm.isExists() method passing in possibly uuid. The uuid is then evaluated as path by hierarchy manager and access permissions are checked, which leads to the error message like

2010-02-03 10:56:01,182 ERROR info.magnolia.cms.core.DefaultHierarchyManager    : User not allowed to Read path [c820b390-2f19-43e9-915a-c544bda13a78]

being logged.
This is quite obtrusive in the log files, specially so since STKUtil.getReferencedContent(), that invokes the above mentioned method in NodeData, is called quite often from templates.

The possible solutions are either to lower severity of the mentioned error message in DefaultHierarchyManager or to make sure that AbstractNodeData determines whether the string contains path or uuid by other means then calling hm.isExists().