any help with showthread

[rob01]

hello.. im currently having some problems with my forum.. if i disable all plugins, i get this error
Warning: in_array() [function.in-array]: Wrong datatype for second argument in [path]/showthread.php(2161) : eval()'d code on line 435

for example here : bbs/showthread.php?t=50, just when showthread.php is called

but if i enable my plugins and i try to modify a thread or creat a new thread adding a web link
i get this error : "this forum cannot contain threads or it is a link please choose another forum.", i know is a plugin.. but im not sure wich one.. since i dont use web link posting restrictions

any idea? :S