Alright, here are my instructions for getting Offline Mode to work if you get the 'Cannot connect to Steam network'/'This action cannot be completed when Steam is in Offline Mode' error. Of course, this will only work if the cause of the problem is the same as mine, and you'll need a hex editor to get it to work.
Fixing Offline Mode
If you have the Offline Mode bug, you will see a message saying 'This action cannot be completed when Steam is in Offline Mode.' To fix it, you will need to edit winui.gcf with a hex editor. For this tutorial, I will be using XVI32, which can be downloaded from http://www.chmaas.handshake.de/delph...vi32/xvi32.htm
1. In XVI32, go to File > Open... and navigate to the steamapps folder (for example C:\Program Files (x86)\Steam\steamapps ). select winui.gcf and click Open.
2. You will see two panes - one with numbers and letters, and one with various symbols. Go to Tools > Options... and in the Appearance tab, change the Number of Columns to 20 (this makes it easier to find the right places).
3. In the hexadecimal panel (the one with the pairs of numbers and letters) go to the start of the second row.
Ensure that the status bar at the bottom says 'Adr. hex 14'. Subtract 1 from the value, remembering that the number is hexadecimal. Next go to the start of the third row (the status bar should say 'Adr. hex 28'). Subtract 1 from this value as well. If you don't know which vlaues to use, see the table below.
4. Save the file, and open Steam again, selecting to go into Offline Mode.
Hexadecimal values can have sixteen different digits in them: 0123456789ABCDEF. This table lists all 256 possible two-digit hex numbers in order. To find out the new value you need, find the existing value in the table. The new value will be the one directly to the left, or at the end of the previous line if there is nothing to the left.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F
30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F
40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F
60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F
70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F
80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F
90 91 92 93 94 95 96 97 98 99 9A 9B 9C 9D 9E 9F
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF
B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF
C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 CA CB CC CD CE CF
D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 DA DB DC DD DE DF
E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF
F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF