I would like to ask what does this error mean when adding a new Available Software Site and installing new software in Eclipse/STS (Spring Tool Suite) using Install New Software?
I am experiencing this problem with the Spring Tool Suite Nightly Build:
http://dist.springsource.com/snapshot/STS/nightly-distributions.html
I am trying to update my STS and reinstall the Welcome Dashboard. When I try to add the following Available Software Site:
http://dist.springsource.com/snapshot/TOOLS/nightly/e4.5
I select all the items in order that they all will be installed,
Then this message is shown in the progress indicator:
Cannot perform operation. Computing alternate solutions, may take a while.
Sometimes I get this message even when trying to update something.
What does it mean? That I have some items already installed? That there's a problem contacting the site?
Means that plugins that you have are conflicting with the ones attempted to be installed. Once it computes the alternate paths, it pops up the next wizard page. you should be able to see what the conflicts are. In this particular case it might be something related to Groovy Eclipse. Try not selecting Groovy and Grails and see if that helps.
来源：https://stackoverflow.com/questions/28983382/cannot-perform-operation-computing-alternate-solutions-may-take-a-while-sts