Every time I hit the start button to perform embroidery, the screen tells me to lower the feed dog - even though it's already down. Is there a way around this?

Well... the manual doesn't say to lower the feed dogs before installing embroidery unit, but carriage operation is likely no different then free motion which requires feed dogs lowered. So I'd say lower feed dogs.

I didn't find exact model but following is what the Brother site gave me for LB6800...
https://download.brother.com/welcome/doch000184/885v31_v32_v33_om04en.pdf

Modern machines do not need much oiling. Perhaps you have over lubricated.

The problem you've explained isn't totally clear. I'll try to give help on your problem.
On embroidery machines the feed dogs are suppose to be down while operating in the embroidery mode.
When you change programs to embroidery the sewing machine recognizes this mode and automatically makes the feed dogs go into the down position.
If you are attempting to operate embroidery and your feed dogs don't go under the plate then: Try the switch that is under the storage unit and switch it to free arm.

Hi, I hope this helps. If it doesn't post again.
"Check:
Place the sewing foot under the sewing foot
holder so that the pins of the foot snap into
the sewing foot holder when the presser foot
lifter is lowered.
Please check that the sewing foot is properly
engaged by raising the presser foot lifter."

Question: Are you using top feed? If so:
"For all sewing jobs with the top feed, only use sewing feet with Cutout at the back (OA, 1A, 3, 4)."

Embroidery foot Part No.: 98-694-840-00 will not work with top feed.

Also, except for eyelets, the darning foot can be used for embroidery.

I'm not sure what you're trying to do :) darn or embroider :); I'm not sure what mode you're working in either; embroidery mode?

Darning with straight stitch
Program 00
Fit darning foot No. 6.
Set the needle at its highest position by turning
the handwheel, and push the pin of the darning
foot fully into the hole of the sewing foot holder
slightly pressing the darning foot between thumb
and forefinger. When doing this, the guide fork
should place itself around the presser bar and the
wire must be behind the fixing screw.
Darning position:
Lower the presser foot lifter pressing it lightly to
the rear until it snaps into the darning position.
Important Only in this position you have the
optimum thread tension for darning.
• Place the darning work in the darning hoop.
• Lower the feed dog.
• Pull up the bobbin thread and hold the threads
when you start sewing.
• Now guide the fabric back and forth evenly;
the length of the darn will be set by the size of
the hole. As you are determining the stitch
length yourself while sewing with the feed dog
lowered, you should sew at an even speed.
When you have reached the width of the dam
aged area, darn over the damaged area again
from right to left.
This guarantees a durable darn.
TIP: The faster you sew, the easier and more even
the darning will be. It you are moving the workpiece
too slowly, small knots will appear on the
wrong side of the fabric."

Whether working with terry-cloth or woven fabric,
with the help of the darning foot and the pro
gram 02 you can embroider initials of your own
design

Drop the feed dog and insert the darning foot.
Put the machine into the darning position.

Spread the fabric in an embroidery hoop and
embroider in accordance with program 02.

Lower feed dog
If the feed dog is not lowered for embroidering, the
machine does not embroider when the foot pedal
is pressed and the message appea rs:
Lower feed dog
ok?
The feed dog must be lowered in embroidery
mode.

look in the operation manual for the feed dog lever and push it to the up position so the feed dogs will come up..

ABSOLUTELY! The XL models of embroidery machines are supposed to automatically lower when you put the embroidery unit on, but I have had an XL-400 and currently have an XL-550 and Quintet, and I have noticed on the latter two that the feed dogs have not always automatically lowered. Incidentally, to lower or raise the feed dogs, the lever (it's in the back) goes DOWN and OVER. If you are having problems getting it move, use a straight blade screwdriver and pop the little tip off--it's not necessary to operating the feed dogs.

Also incidentally, when you raise the feed dogs, you have to turn the hand wheel towards (ALWAYS towards you for anything) several times to get the feed dogs to actually pop up. You'll hear when it does that. They lower right away, though.

had a quick look at the manual for this at www.singer.com and I'd say your machine doesn't have the function to lower the feed dogs, many don't. It shows a darning plate which goes over the feed dogs to sew on buttons so if you are wanting to do free motion embroidery or similar, then use this plate to cover up the feed dogs.

The embroidery carriage automatically lowers the feed dogs when put in place

Lower the feed dog. THere is a button on the right side of the machine; lower left corner. Push it in.

If you look at the back of the machine you should see the button that will let you lower the feed dog. It looks like you slide the button one way to lower and then the other way to raise the feed dog.

To make it a bit easier just go to the following web site and move down to the pictures as there is one showing the back of the machine. The button would be on your right:

http://www.ebay.com/itm/JANOME-MEMORY-CRAFT-5700-SEWING-EMBROIDERY-MACHINE-QUILTING-TOO-ADDED-EXTRAS-/301088834718