By Justin Parkinson
BBC News education reporter, in Birmingham
Lifelong learning is an idea central to the government's plans for education.
Colleges say they are torn between competing priorities
Skills must be improved if the UK is to compete with other economies, it says.
Further education - the network of colleges up and down the country - has been told to become more business-friendly.
The government also wants the sector to increase its budget by attracting firms eager to train their workers.
But, say colleges, they are being asked to be all things to all learners.
Ministers also want them to offer more vocational training to 14 year olds.
Budgets are being stretched and adults who want to gain skills or change careers are suffering.
Danny Clough, the principal of Colchester Institute, which has 14,000 students, feels like the lettuce in a sandwich of pressures.
He told the BBC News website: "I'm turning away 1,000 students a year at the moment.
"The money problems mean we are doing this in areas where there are a shortage of skills, like construction.
"We have a lot of demand on one hand, but not enough supply on the other. It's very ironic."
Mr Clough, and other principals gathered at the Association of Colleges' annual conference in Birmingham, said they wanted to offer courses for the whole community.
But some adult learners had to pay £200 a year for access courses.
Meanwhile, other government initiatives, aimed at businesses, were offering free skills training, meaning their own funds were suffering.
Mr Clough said: "Most of our adult learners are rather older. They are usually in their 30s, 40s or 50s.
"Often it is a second chance for them. We are also having to cut IT courses, which are popular among older students.
"This is not what the government is aiming towards."
Helen Parr, principal of Oaklands College, Hertfordshire, looks after 14,000 adult learners.
She said: "There is a huge practical skills shortage in my area, especially in parts such as plumbing and brickwork.
"And it looks like that demand is going to stay."
Ms Parr criticised the government's accreditation only of certain courses, resulting in different levels of funding.
She said: "What employers often want from training is short, quick fixes to enable people to do jobs now.
"They don't always want longer-term, accredited programmes where we get the funding.
"The priorities are not always right. A lot of adults also want to do short courses - like plumbing for beginners - which improve their skills, but which are not accredited."
According to the AoC, funding shortages mean that fees payable by adults or companies will rise by 40% over the next 18 months.
David Lawrence, principal of Easton College, set in a largely rural area of Norfolk, has another problem with the government's funding strategy.
Some 90% of employers in the area have fewer than six staff.
On top of the money spent on training, they cannot spare workers for long enough to take time-consuming courses.
Mr Lawrence said: "A lot of agricultural and other firms are having to change working practices to fit in with Europe.
"It means there's a lot of work to do with small employers.
"The government has to be consistent and not offer bits of free training elsewhere while expecting us to take on students."
The AoC is calling for an increase in funding for further education. Its conference lasts until Thursday.
The Department for Education and Skills has said more funding is being provided - but that colleges must do more to raise funds themselves from businesses and individual students.
"The government cannot and should not be expected to fund everything," the Education Secretary, Charles Clarke, told the conference.