WowAce

Since the patch I am getting this error if I try to move decursive while in combat 

3x [ADDON_ACTION_BLOCKED] AddOn 'Decursive' tried to call the protected function 'DcrMUFsContainer:StartMoving()'.
[*Dcr_DebuffsFrame.xml:106_OnMouseDown]:4: in function <[string "*Dcr_DebuffsFrame.xml:106_OnMouseDown"]:1>

Locals:
self = DcrMUFsContainerDragButton {
isMoving = true
}
button = "LeftButton"

It was overlapping another UI element and I couldn't move it, I was just getting this error. I checked that its up to date and reloaded my interface and it continues to happen. I just tested it at the training dummies too. 

Can you try with just Decursive enabled?

Yes, I have disabled every other addon except decursive and when I am in combat, I am unable to move the little window like I have always done by pressing alt and left clicking on the little mover square above the decursive frame. Since I do not have bugsack installed, instead of the detailed message, I just get the yellow text in chat "Interface action failed because of an AddOn"

ok thanks for the details, I'll take a look at this asap

Well this actually never worked I'm afraid, or did not for many years. The MUFs are using "protected" frames (frames that can cast spells and target units) and those cannot be moved while in combat (to prevent automation). There is supposed to be a way to do it but since Decursive is doing some complex stuff with this frame positioning it cannot be used apparently. I've made a few attempts but even the basics doesn't appear to work.

There is currently a bug that if you are moving the MUFs while entering in combat it will get stuck to your mouse pointer until the end of the combat. It'll be fixed in next release.

Do you know of any other combat add-on able to move such protected frames while in combat?

No I don't have anything like that. I do wish I knew what changed because when another UI element overlaps with decursive it makes it really hard to see the frames and if I can't move it during a boss fight its pretty frustrating. 

What kind of other UI element can overlap with Decursive?

My weakauras and cell raid/party frames overlap decursive sometimes. For example, I usually have cell and decursive put nicely to the left of my class weakauras setup for a 5 man. But when I join a raid, decursive gets as many squares as raid members and then it overlaps on top of my weakauras. So if I am in combat right away, I can't move them and I get this LUA error. 

Have you tried the various options to organize the MUFs? (you can anchor them differently so they 'grow' without moving the handle)