How to C2C Get Custom Field Values and Customizable Post Listings work together

I′m trying to make an image gallery in my WordPress. I′ve using the excerpt to show the thumbnails of images, but when I make an export of posts, custom fields are saved, but not the excerpts. So, I′ve decided to use custom fields to show the thumbnails, but I can′t make it work with the regular method to show the custom fields content.

With using excerpts for thumbnail, the C2C Customizable Posts Listings was my weapon of choice. I used that piece of code to show the thumbnails:

<?php c2c_get_recent_posts(1000, "<a href='%post_url%'>%post_excerpt%</a>", $cat); ?>

(I use the cat variable to get the category id with <?php $wp_query->query_vars[‘cat’]; ?>)

It works really perfect. But when I decided to get rid of excerpts and start to use custom fields, and the method described on the codex to show the custom field values don′t work for me, I tried the C2C Get Custom Field Values. The problem is to show the values of the custom field inside the c2c_get_recent_post function. I tried this piece of code, but results on a white screen:

<?php c2c_get_recent_posts(1000, "<a href='%post_url%'>" c2c_get_custom('thumbnail', '<p>', '</p>', '') "</a>", $cat); ?>

I still a little noob in PHP, but I think that one function can be called inside another function, but I don′t know how to make that, or if it can be possible.

If someone can help me, I will appreciate it for the rest of eternity.

Thanks.