Do you have a errors/local.xml file?
This file dictates whether the error is printed to the screen or alternatively you cen set it to email the error to you.
Here's an example
<config>
<skin>default</skin>
<report>
<!--
"action" can be set to "print" to show exception on screen and "email"
to send exception on specified email
-->
<action>print</action>
<!--
in "subject" you can set subject of email
-->
<subject>Store Debug Information</subject>
<!--
"email_address" admin email address
-->
<email_address>user@example.com</email_address>
<!--
"trash" is handle about trace info
value "leave" is for store on disk
value "delete" is for cleaning
-->
<trash>leave</trash>
</report>
</config>
Change the <action> to email and put your email address into <email_address>.
This will stop errors being printed to the screen.
