In comments there are entity fields. Cron, cache and permission were rebuilt. Nothing helps. In version 7.13 there are no issues.
When a node with comments is viewed, this warning is shown:

Notice: Undefined index: #submit in function inline_entity_form_form_alter() (line 792 in file sites/all/modules/inline_entity_form/inline_entity_form.module).
Warning: array_merge() [function.array-merge]: Argument #2 is not an array in function inline_entity_form_form_alter() (line 792 in file sites/all/modules/inline_entity_form/inline_entity_form.module).