Yesterday, I got error as:
1062 Duplicate entry 'zc_7eb4ed1f36d90140477d9474b61e0e26' for key 1
in:
[insert into zen_db_cache set cache_entry_name = 'zc_7eb4ed1f36d90140477d9474b61e0e26', cache_data = 'a:568:{i:0;a:2:{s:6:\"cfgkey\";s:10:\"STORE_NAME\";s:8:\"cfgvalue\";s:13:\"Shop In Nepal\";}i:1;a:2:{s:6:\"cfgkey\";s:11:\"STORE_OWNER\";s:8:\"cfgvalue\";s:5:\"Akh il\";}i:2;a:2:{s:6:\"cfgkey\";s:13:\"STORE_COUNTRY\";s:8:\"cfgvalue\";s:3:\"149\ ";}i:3;a:2:{s:6:\"cfgkey\";s:10:\"STORE_ZONE\";s:8:\"cfgvalue\";s:1:\"1\";}i:4;a :2:{s:6:\"cfgkey\";s:22:\"EXPECTED_PRODUCTS_SORT\";s:8:\"cfgvalue\";s:4:\"desc\" ;}i:5;a:2:{s:6:\"cfgkey\";s:23:\"EXPECTED_PRODUCTS_FIELD\";s:8:\"cfgvalue\";s:13 :\"date_expected\";}i:6;a:2:{s:6:\"cfgkey\";s:29:\"USE_DEFAULT_LANGUAGE_CURRENCY \";s:8:\"cfgvalue\";s:5:\"false\";}i:7;a:2:{s:6:\"cfgkey\";s:25:\"LANGUAGE_DEFAU LT_SELECTOR\";s:8:\"cfgvalue\";s:7:\"Default\";}i:8;a:2:{s:6:\"cfgkey\";s:27:\"S EARCH_ENGINE_FRIENDLY_URLS\";s:8:\"cfgvalue\";s:5:\"false\";}i:9;a:2:{s:6:\"cfgk ey\";s:12:\"DISPLAY_CART\";s:8:\"cfgvalue\";s:4:\"true\";}i:10;a:2:{s:6:\"cfgkey \";s:32:\"ADVANCED_SEARCH_DEFAULT_OPERATOR\";s:8:\"cfgvalue\";s:3:\"and\";}i:11; a:2:{s:6:\"cfgkey\";s:18:\"STORE_NAME_ADDRESS\";s:8:\"cfgvalue\";s:31:\"Shop In, cache_entry_created = '1166808336']
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Then I logged into my phpMyAdmin and there in the table zen_db_cache, there was already that key exits. Then I delete that record and my site was back.

But today, I again find this same issue and looked at the zen_db_cache table. The same problem of duplication.
Could anyone help me out what is causing this?

Thanks