We have confirmed the following issue is occurring.
Please refrain from performing the following actions, and be sure to read the description of the issue carefully.

[Details]
If you summon your retainer while queued in the duty finder, get matched, and zone to the instance with your retainer still summoned, you will become unable to summon your retainer thereafter.

[Temporary Solution]
We are sorry, but ask that you take the following steps until this issue has been addressed.
- If you have summoned your retainer while being matched in the duty finder, please return them before entering the instance.
- Refrain from summoning your retainer while queued in the duty finder.

The issue is being investigated and addressed, and we ask for your patience and understanding as we strive to resolve this promptly. We are also currently investigating ways to help those who have currently already become unable to summon their retainers.

We apologize for any inconvenience this may cause.

We have confirmed the following issue is occurring.
Please refrain from performing the following actions, and be sure to read the description of the issue carefully.

[Details]
If you summon your retainer while queued in the duty finder, get matched, and zone to the instance with your retainer still summoned, you will become unable to summon your retainer thereafter.

[Temporary Solution]
We are sorry, but ask that you take the following steps until this issue has been addressed.
- If you have summoned your retainer while being matched in the duty finder, please return them before entering the instance.
- Refrain from summoning your retainer while queued in the duty finder.

The issue is being investigated and addressed, and we ask for your patience and understanding as we strive to resolve this promptly. We are also currently investigating ways to help those who have currently already become unable to summon their retainers.

We apologize for any inconvenience this may cause.

[Edited on Nov. 10, 2015 at 5:15 (PST)]
Players affected by this issue will be able to summon their retainers again after this issue has been resolved, so we ask that you please wait until this issue has been resolved.

[Edited on Nov. 12, 2015 at 3:45 a.m. (PST)]
This issue has been addressed with the Emergency Maintenance which took place on Nov. 11, 2015 11:00 p.m. to Nov. 12, 2015 1:45 a.m. (PST) / Nov. 12, 2015 9:00 to 9:45 (GMT).
You are now able to summon your retainer as normal.
There was also issues wherein items posted by retainers on the Market Board would fail upon purchase, but this has also been addressed.
We apologize for any inconvenience caused.