I am using the model builder in ArcMap to create zonal statistics as table (daily time series-so iterating rasters in the beginning). The tool works fine, it's just that I have another additional step, where I want the zonal statistics table to be sorted in descending order (for the polygon IDs) rather than the default ascending order. So, for that I added the sort tool in the model, the tool is then linked to the append tool to finally merge all the zonal tables into a single table. In all this I am getting an error in the append tool which states that all the inputs need to be in the same format. Although, in the sort tool I am setting the sort output as table and target dataset in Append tool is also a .dbf table.
I don't know if your error is related to this issue but your model logic is flawed. The append tool takes a LIST of datasets as input, your model is feeding one at a time on each loop of the iterator. Not only is this wrong but highly inefficient. You need to feed the output of sort into a collects value tool, expose that as a parameter and then make that a sub-model in a master model with a single append tool. There are many Q&A on this forum where people are making the same mistake. An answer to this question provides a link to a you tube video, or you could just look at the help file and understand sub-modelling and when to use the collect tool. Be aware don't make the error of simply linking to the collects value tool, that part must be a model embedded in a master model.
I don't know if that solves your error but at least you will be doing it right!