Really sorry for not replying sooner! Better late than never I guess?
Off topic, but another problem I had was with literally updating it. I had to download it from the website and install it that way, as it came up with an error when trying to update from inside paint.net. Not too much of a problem and might just be something to do with my firewall but anyway,
Oh, and disabling the Hardware Accelerated Rendering (GPU) worked for me as well.
Here is my diagnostics info:
Application paint.net 4.0 (Final 4.0.5288.36565)
Build Date 24 June 2014
Hardware accelerated rendering (GPU) True
Animations True
Language en-US
OS Windows 7 Service Pack 1 (6.1.7601.65536)
.NET Runtime 4.0.30319.18444
Physical Memory 8,074 MB
CPU Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
Architecture x64 (64-bit)
Process Mode 64-bit
Speed ~2394 MHz
Cores / Threads 8
Features DEP, SSE, SSE2, SSE3, SSSE3, SSE4_1, SSE4_2, XSAVE
Video Card NVIDIA GeForce GT 650M
Dedicated Video RAM 1,990 MB
Dedicated System RAM 0 MB
Shared System RAM 2,048 MB
Vendor ID 0x10DE
Device ID 0x0FD1
Subsystem ID 0x05521028
Revision 161
LUID 0x0000A6C8
Flags None
Outputs 1
Video Card NVIDIA GeForce GT 650M
Dedicated Video RAM 1,990 MB
Dedicated System RAM 0 MB
Shared System RAM 2,048 MB
Vendor ID 0x10DE
Device ID 0x0FD1
Subsystem ID 0x05521028
Revision 161
LUID 0x0000B33C
Flags None
Outputs 0