Summary
Environment
All versions of Designer/Server
PostgreSQL 9.4
Cause
This error (or similar) indicates that you have a character that can't be encoded properly:
Error: Input Data (1) Error SQLExecute: ERROR: character with byte sequence 0xef 0xbc 0x8c in encoding "UTF8" has no equivalent in encoding "WIN1252"
Using a character that has no ASCII translation can throw an error when connecting to PostgreSQL with the PostgreSQL ANSI driver. The character has a UTF-8 or UTF-4 translation but can't be handled by the PostgreSQL ANSI driver.
Resolution
PostgreSQL has multiple choices for drivers: ANSI and UNICODE. Connect to PostgreSQL with UNICODE driver and it should resolve the UTF-8 encoding error.