We recently ran into some issues while trying to run the Remove Duplicate Centerlines process in our Roads and Highways implementation, which is currently using ArcGIS 10.5.1. I figured I'd document it here in case someone else encounters a similar problem.
There were two attempts to run the tool that halted due to error. The slightly confusing part is that both of these runs had a different error message. The first had a message stating "An expression of non-boolean type specified in a context were a condition is expected, near ','.
And the second run had this message, stating "Unable to update original centerlines: Sequence contains no matching element"
The errors were caused by features in the Centerline feature class that had a Null value for the ROADWAY_GUID. These features are artifacts from sloppy editing, to be honest. Centerline features that are created but never used as apart of a route will have a null GUID. We found that removing the problem features from the current database version was not enough, but rather the features had to be removed from all active database versions.
It turns out we encountered a similar issue in the past. The Remove Duplicate Centerlines tool would hang without an error message. We submitted a support ticket about the issue, and soon after a bug was submitted and fixed by Esri.
The fix should be in ArcMap >= 10.6. Maybe there's a more helpful error message on newer versions of the software. Has anyone using 10.6+ ran into this issue?