error ltdl

[sonjaya]

dear all 

i use freebsd 6.0 to install openldap , when i
configure from source not port i get error such like
this the error :
ecking dependency style of cc... (cached) none
checking for cc depend flag... -M
checking for afopen in -ls... no
checking ltdl.h usability... no
checking ltdl.h presence... no
checking for ltdl.h... no
configure: error: could not locate libtool ltdl.h

how to solved that .

My regards

My Regard's

SONJAYA