Cutting with 455 rancher chain locked up took cover off ,replaced chain and put cover on still locked up

Husqvarna - IPL, 455 Rancher/ 460, 2006-02, Chain Saw (example - may not be your saw):
http://weborder.husqvarna.com/order_static/doc/usa/2006/I06000/I0601076.pdf
See Detail A, pn 503 89 08-02. You can use a Crescent Wrench on one of the ears (left end) to reset it. With the cover positioned with pn 503 89 08-02 in the upper left rotate it CW until it nests, to reset it.

This works quite well:
Reset Chain Brake by Dolfoff
Please follow this link, http://www.fixya.com/support/t3102817-re_install_side_cover_after_chain
Cursor down to “Best Solution”, while there click the “Was this helpful? [Yes]” button
If you do not have a vise a large C clamp to a work surface might work, you may still need a block or two of wood.

You can download the IPL for you saw here:
HusqvarnaUSA.com
http://www.husqvarna.com/us/homeowner/support/download-manuals/
Enter the 3 digit model number (no XPs, Es, just the numbers)
Serial number decode – useful when downloading IPLs and Manuals
06 1500198
06 = year produced – 2006 (single digit before 2000)
15 = week produced - March
00198 = 198th unit Husky produced that week

I will wager you will NEVER again remove the cover with the brake set. Me either! Good Luck. HTH
Lou