[Exim] TLS error message

Im getting this error when enabling TLS. What am I doing wrong? It isnt
obvious from the error.... Have read the manual and so on and cant find
anything that might be relevant.

2002-12-19 18:20:59 TLS error on connection from einsteinium.btinternet.com [194.73.73.147]
(SSL_CTX_use_certificate_chain_file): error:02001002:system library:fopen:No such file or directory

Ive got my real (non self signed) certificates in /usr/local/ssl/certs

configure says:

tls_certificate = smtp.crt
tls_privatekey = smtp.key
tls_advertise_hosts = *

smtp.crt and smtp.key are located in /usr/local/ssl/certs?

smtp.crt and smtp.key look to be the correct format as evidenced by
comparing them with a self sign certificate.

Also, separately from this problem, is it correct to do:

cat smtp.key smtp.crt > smtp.pem ? Is a .pem really simply a concatenation
of .key and .crt therefore I can use the tls_certificate = smtp.pem
without having tls_privatekey in the configure file?

Thanks

Andy