Since FishEye/Crucible 2.6, FishEye has switched from Crowd's SOAP API to its REST API (see FE-3705). This effectively makes FishEye only compatible with Crowd 2.1+ (see http://confluence.atlassian.com/display/CROWDDEV/Crowd+REST+APIs for more info).

However the compatibility was not documented:

• https://answers.atlassian.com/questions/6484/fisheye-2-6-x-and-crowd-2-0-2
• http://confluence.atlassian.com/display/FISHEYE/JIRA+and+Crowd+Authentication?focusedCommentId=246481449#comment-246481449