Problems with using "lookup fields" and custom "lookup fields"

Problems with using "lookup fields" and custom "lookup fields"

Dear Zoho team, 

I wold like to use various lookup fields to refer to different types of customers within the contact module, however I do not get it running. Everthing works fine until I really want to use it, because the button to modify the field within a contact does not appear when sliding with the mouse over it.  

First, I just wanted to use the module vendor, which is pre-defined as a lookup field in the module contact. Then, I tried the same - just using customers instead of vendors - and it worked out. ...Weird!!!! Isn't it???

Then I thought ok let's use customers instead and define different types of customers. To be more precise, I want to refer to 2 or 3 different "types" of customers from my contact module. ALthough I set up the "custom lookup field" as described within the documentation...it is not working. 

Here is an other link which explains it well, but just won't work...any ideas??  
http://www.datawebcoder.com/codeByLanguage/1033/ZOHO_CRM_How_to_use_lookup_field.aspx