Hi lubo,
The problem you observe with Debug RAM build is that there are sections in the Debug Configuration (Flash) that are not present in RAM build (typically reset vector section, ROM->RAM copy sections,...)
Since your Debug (Flash) build configuration project startup routines rely on custom linker symbols that contain e.g addresses or of these sections (OS_NONCACHE_BSS_START...) - these symbols are missing for RAM configuration.
You need to define these symbols in 57xx_ram.dld linker file and probably use conditional compilation to skip startup ROM->RAM copy-down routines for RAM project.
Hope it helps.
Stan