Kepware Drivers > G-L Drivers > GE SNP > Error Descriptions > Blocked Reads Error Messages > Unable to read '<number of bytes>' bytes starting at address '<tag address>' on device '<device name>'. Service request mailbox type is either undefined or unexpected
Unable to read '<number of bytes>' bytes starting at address '<tag address>' on device '<device name>'. Service request mailbox type is either undefined or unexpected
Unable to read '<number of bytes>' bytes starting at address '<tag address>' on device '<device name>'. Service request mailbox type is either undefined or unexpected
Error Type:
Warning
 
Possible Cause:
The service request mailbox is either undefined or unexpected.
 
Solution:
Make sure that a valid mailbox type has been specified. Valid values used by client SNP implementations are 0xC0 and 0x80. Valid values used by server SNP implementations are 0xD4, 0x94, and 0xD1.
 
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