Do you have stuck Documents, OldDocuments, and/or DocumentExports stuck in the corner of you map? Are workman unable to move these items? If you answered yes to both questions then your prison save file needs editing.

1) First open your prison save with Notepad or other similar program. (saves normally are in C:\Users\YOURUSERNAME\AppData\Local\Introversion\Prison Architect\saves)

2) Press Ctrl-F and search for DocumentExport

3) Remove any lines that look like:
BEGIN "" Id.i 287 Id.u 4900486 Type Stack SubType 0 Or.y 0.0000000 Loaded true CarrierId.i 417 CarrierId.u 149388 Contents DocumentExport Quantity 25 LastAccess 95253.95 END

And

BEGIN ""
Id.i 494
Id.u 5302782
Type Stack
SubType 0
Pos.x 88.15743
Pos.y 43.71753
Or.x 0.1287410
Or.y 0.9905708
Carried 5
CarrierId.i 1621
CarrierId.u 5249231
Contents DocumentExport
Quantity 4
LastAccess 95727.52
END

4) Repeat for OldDocuments

5) Save the file and restart Prison Architect. It should work assuming you did everything properly!

Alternatively, you can just start a new prison.