I realise this is old but I just had a similar issue/same error after reading lat long data from a spread sheet. The resolution was in to insert CsmapReprojector after the reader to reproject before writing out the new data set.
Worked like a charm.
I have been having the same error when trying to use the Reprojector transformer. I understand that your post is older but am wondering if you were able to find a solution? I am going through the training tutorials that FME-ESRI have provided and any time I try to use this transformer it fails. Any Ideas would be helpful.
I ran into the same issue as you when taking the training (Desktop Basic 2019, BestPractice-Ex1 and again with Desktop Advanced 2019, FMEReview-Ex1 and Attributes-Ex2). I got this same error with Reprojector.
Thank you for this information. I was not aware that Esri had its own reprojector. Also I did have some success early on with finding the alternate values in ESRI and using them.... example LL83 would work using EPSG:4269, and UTM83 worked using EPSG:26910. However sometimes it would also cause other errors of incompatibility. Again thank you, for the ideas. I will share with my colleagues.