If we include the build system within the SDK (see bug 6435) there are some characters that cannot appear in the installation path, so we need to check for these. Unfortunately one of those characters is + and this commonly appears in the SDK default install path when it comes from Poky in-development value for DISTRO_VERSION - e.g. "1.6+snapshot". Either we eliminate the restriction or we need to somehow ensure that + isn't in the default install path as well as adding a check.
Fix merged to master: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=f5f9185344df1408e4bccfecd352373522721910