@MorganDavis0102 Error 999999 is often, but not exclusively, related to something in a file name, path, data set name, or even field name that Pro finds offensive. It can be a space or non-standard character in a folder name, too long a network save path, funky attribute field name (data supplied from non-Esri sources that allow bad things exist), number of attribute fields, etc.
Check all your source & destination paths, and then go through the data names, etc.
It may pay to copy everything to a local folder (e.g. C:\tmp_GIS and not inside a Windows abstracted location such as Documents) and then use short data names for any output. Go hardcore 8 characters max.
If you can get it working then you know your input data itself isn't the issue and you can then move the process back to your main data location step by step to see where it fails.
If you are currently processing some input data and wanting to use the resultant in-memory compilation as the input to your tiling process I would strongly recommend saving the in-memory data to a proper location first, before using it for something like tiling.
If Pro crashes for any reason (that never happens......) your in-memory data is gone and you have to recreate it from scratch.
