Oracle Message PGA-20910 - communication error: CPI-C string failed, rc = number, errno = number

ERROR	communication error: CPI-C string failed, rc = number, errno = number
CAUSE	An unexpected communication error occurred while executing the specified CPI-C function . The CPI-C function return code and system error number are provided in the message text. The CPI-C function return codes and system error numbers are described in the vendor documentation.
ACTION	Determine the cause of the communications error, correct it, and rerun the transaction.