Whenever I insert a datavalue, the command block says the following: An unknown error occurred while attempting to perform this command
Inserted command: /particle blockcrack_1_1 ~ ~ ~ 1 1 1 0.5 20
keep data value away (/particle blockcrack_1 ~ ~ ~ 1 1 1 0.5 20) works just fine, as does the iconcrack with data value (/particle iconcrack_1_1 ~ ~ ~ 1 1 1 0.5 20).
See MC-61033