Please provide a bit more detail of your problem.
1. Which version of Adobe Reader are you using ?
2. Are you trying to save a locally created PDF or PDF from web browser?
3. Are you trying "save " or "save as" ?
4. you have asked that on some of the computers it is working fine, are you trying to save the same PDF on other computers too ?
please also provide the information that which operating system you are using.
I'm getting the same error message.
In response to your questions:
1. Adobe version 10.1.3
2. I'm using an application that has the option to publish to pdf, when I'm prompted to Save or Open the pdf document, I select 'Open'. Once the document is opened in Adobe Reader, I try to save it.
3. I'm trying to 'Save as...', the 'Save' option is greyed out
4. Operative system: Windows 7 (64-bit)
Any suggestions to resolve this would be much appreciated.