As of Icinga 1.4, there is a new cgi.cfg option:
When this option is enabled you have to put a comment for a \'Recheck\' of a host/service so nagstamon does not bring up a box to put a comment and the command fails
Sounds logical.... well, I will care for this issue next time there is some Nagstamon devel time. A workaround might be to add some command field into the Icinga recheck CGI URL call... but take care, expecially Icinga wants to have an exact order of cgi command keywords - I guess there is some testing required.
Should work at least with 0.9.10.rc1