Cannot drag tasks to columns on active sprint

[Jason___]

Hello. This is driving me mad. I cannot drop tasks on the active Sprint board between columns. When I try, it simply does not let me drop them anywhere, and the columns do not turn green when I hover a task over them (whilst dragging). Essentially they appear disabled/ready only. I can add tasks no problem, and I can change their state manually (e.g. from To Do to In Progress). This does not really help though as I have a few columns that map to the same state.

Now, on past or future sprints I can move tasks around no problem. That's obviously no use but its a point to note in my diagnosis of the issue.

Further on from this, another project works just fine for me (in it's active sprint).

Working example:
On Friday, the current Sprint (ending that day) does not let drop a task on another column.
On Friday I create a new empty Sprint to start Monday.
I enter a test item and it lets me move it around columns.

On Monday, we plan our Sprint, drag some items forward from the previous sprint and also from the backlog.
During this, I cannot now drop between columns.

I am a member of the project team and also a Project Admin, along with being thoroughly confused.

Thanks for any thoughts.

[#2 · Accepted solution]

There's nothing like writing something down or saying it out loud to give you an idea! This is sorted now. For anyone reading this in the future, the solution / reason was that one item was causing the issues.

Removing the item, sorted the whole board. This item had been brought forward from the previous sprint.

I am guessing this may be because that since the item was created and added to a sprint, I have changed some of the configuration of the sprint board and also the Scrum inherited process (new columns, added some item type to the process etc). It must have got itself (or by me) tied in knots. Not certain, but that's all I can think of.

All sorted now though. I recreated the item from scratch (it was only a small item anyway).