I had this weird error the other day, when all my report definition .rdl files seemed to get corrupted somehow. I’m not sure what caused it but it might have been something to do with Tortoise SVN.
The error was something like “[rsInvalidReportDefinition] SSRS the report definition is not valid. Details: ‘.’, hexadecimal value 0x00 is an invalid character”. A screenshot is below:
When I opened the rdl it looked fine, and when I viewed the source of it in Visual Studio it also looked fine. But the telltale sign was that I could not delete the last character in the .rdl file, a ‘>’ which closed off the final </Report> tag. In the end the fix was quite simple, all I did was delete that last </Report> tag and type it in again.
Hope this helps someone.
Matt's work blog 
hi
I just recently ran into the same issue with SSRS reports and .rdl file.
I did what you suggested. I opened the .rdl file and deleted the last tag and re-typed it, but that didn’t solve the issue. I was wondering if you came across another fix besides the suggestion above since you published this article in 2010
thank you
Sorry man, but I haven’t used SSRS in years.
Hi Matt
After I researched even more on this issue(I have to create an automated deployment for rdl files here at work), i found out that if you try to deploy the report using rs.exe using the command line, you need to use a .rss file which is written in VB.
To make a long story short, the issue is in the array definition in the VB script and the code to fix is this:
ReportDefinition = New [Byte](rdlfile.Length -1) {}
note the -1, that’s what fixed my issue and now i don’t get the error above.
Just wanted to post this in your blog, since it is referenced in the Microsoft SQL server forum as one of the possible solutions
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/a027541d-f70f-4f2e-bce6-7bef7630edf9/getting-a-hexadecimal-value-0x00-error-in-all-my-rdl-files-why?forum=sqlreportingservices
and the article for the fix is here: https://connect.microsoft.com/SQLServer/feedback/details/331311/rs-exe-fails-to-deploy-a-report-upgraded-from-sql-server-2005-reporting-services-report-definition-is-not-valid
thanks!
Amauri
Just thanks, saved me hours
Bl**dy brilliant, thank you. I’ve been wrestling with this problem for a while. The -1 solution sorted it for me. I owe you a beer.
Amauri. You saved my day :D
Amauri,
You’re a Champion. Thanks a lot – that did it for me.
Brilliant Buddy.. Thanks A lot
Thank you you’re ‘s gem
Thanks Amauri…
Awesome! Thanks a lot Amauri!
Amauri you are a genius my guy.
Thank you. worked for me
OH. MY. GOD.
THANK YOU THANK YOU THANK YOU.
I have gone in circles trying to fix this. You’re a god send.