Please tell us about the following points.
Is it writable from a USB cable and PSoC Creator instead of MiniProg3 and PSoC Programmer?
Also, please let us know the version of PSoC Programmer you are using.
And do you have a screenshot of the error content?
Do you know the part number of PSoC mounted in CY8CKIT-050?
Is the part number used CY8C5868AXI-LP035?
The older CY8CKIT-050 uses an unsupported PSoC5 instead of the PSoC5LP.