I'm trying to enable Clear Text logins for imapsync, but I'm getting a strange error:

ERROR: service.FAILURE (system failure: unable to modify attrs: [LDAP: error code 80 - Other])

Same error happens either on the web interface or with the cli


Code:
[zimbra@zimbra1 root]$ zmprov mcf zimbraImapCleartextLoginEnabled TRUE
ERROR: service.FAILURE (system failure: unable to modify attrs: [LDAP: error code 80 - Other])
[zimbra@zimbra1 root]$ top
top - 17:13:39 up 13 min,  1 user,  load average: 0.28, 0.38, 0.23
Tasks: 235 total,   1 running, 233 sleeping,   0 stopped,   1 zombie
Cpu(s):  4.8%us,  0.5%sy,  0.0%ni, 94.3%id,  0.4%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   4043180k total,  1877060k used,  2166120k free,    25168k buffers
Swap:  2096472k total,        0k used,  2096472k free,   297444k cached