With Cura 2.6.52, a number of materials are missing out of the materials list for the TAZ 5 with single extrude.
I looked at one of the material files (polylite PLA) and found that the TAZ5 single extruder isn’t listed.
The file is listed below and TAZ 5 is missing for the single extruder (lulzbot_taz5)
Thank you for the report, this is not intentional and we have opened a bug ticket to look into it, and get it sorted for future releases: https://code.alephobjects.com/T1363
As for now, go ahead and use the Verbatim or Village Plastics PLA profiles. The Polylite PLA profile was based on these, and should be fairly close.