Data Source Error

[user2321]

I have previously been able to connect to my Postgres DB through the powerBI gateway - I just added a new table from there and now I get this error 

Data source error{"error":{"code":"DM_GWPipeline_Gateway_InvalidMashupConnectionString","pbi.error":{"code":"DM_GWPipeline_Gateway_InvalidMashupConnectionString","parameters":{},"details":[],"exceptionCulprit":1}}} 

I've tried many things but Im not sure why this has happened. It fails for the tables where I have these sort of PowerQuery steps:
- filtering rows

- sorting rows

- removing duplicates

- reordering columns 

- and adding rank columns (Table.AddRankColumn(#"Filtered Rows2" , "initial_rank", {"rank_final"}, [RankKind=RankKind.Competition])

Has anyone got any ideas?

Update: I have traced this step by step (Table.AddRankColumn(#"Filtered Rows2" , "initial_rank", {"rank_final"}, [RankKind=RankKind.Competition])
Thsi is it and I cannot figure out whats wrong with it.

[lbendlin]

Have a look at the query diagnostics.  Power Query may try to fold that step and fail to do so.

Note:  stuff like reordering columns or ranking is better avoided. Do that in the UI if you must.