SQL Server: converting UniqueIdentifier to string in a case statement

We have a log table that has a message column that sometimes has an exception stack trace. I have some criteria that determines if the message has this. We do not want to show these messages to the customer but instead have a message like:

> Internal Error Occured. Contact US > with reference code > xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

where xxx etc is a guid column in the table. I am writing stored proc like this:

declare @exceptionCriteria nvarchar(50)
select @exceptionCriteria = '%<enter criteria etc>%'

select LogDate,
       case
       when Message like @exceptionCriteria
       then 'Internal Error Occured. Reference Code: ' + str(RequestID)
       else Message
       end
  from UpdateQueue

RequestID is a Guid datatype in SQL Server and does not convert to string here. I've seen some code on how to convert a Guid to string, but it is multi-lined and I don't think it would work in a case statement. Any ideas?

I think I found the answer:

convert(nvarchar(36), RequestID)

Here's the link where I found this info:

http://msdn.microsoft.com/en-us/library/ms187928.aspx

It is possible to use the convert function here, but 36 characters are enough to hold the unique identifier value:

convert(nvarchar(36), requestID) as requestID

Edit: yes, as noted in the comments, char, or nchar, or any function that can properly manipulate ASCII character tables would do the trick. Then, my excuse is that I usually work in a multilingual/multialphabet environment, and the rule is to go for nvarchar, always. That's my no-brainer way of doing things, sorry. And, if one of these days, some database software starts to generate unique identifier with non-ASCII elements, I will be ready.

In my opinion, uniqueidentifier / GUID is neither a varchar nor an nvarchar but a char(36). Therefore I use:

CAST(xyz AS char(36))

Instead of Str(RequestID), try convert(varchar(38), RequestID)