memory error – Please Help

Hi guys

i having trouble with all wordpress installations on my server

wordpress itself installs fine but if i try adding themes or certain plugs iget the following error

Fatal error: Out of memory (allocated 18350080) (tried to allocate 1103733 bytes) in /home/wordshou/public_html/word/wp-includes/class-http.php on line 1426

I have checked teh php.ini file on the server and the memory limit is 250MB

Can anyone help with this please??

Thanks guys
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